Brakes

The modern automotive brake system has been refined for over 100 years and has become extremely dependable and efficient.

The typical brake system consists of disk brakes in front and either disk or drum brakes in the rear connected by a system of tubes and hoses that link the brake at each wheel to the master cylinder. Other systems that are connected with the brake system include the parking brakes, power brake booster and the anti-lock system.

When you step on the brake pedal, you are actually pushing against a plunger in the master cylinder, which forces hydraulic oil (brake fluid) through a series of tubes and hoses to the braking unit at each wheel. Since hydraulic fluid (or any fluid for that matter) cannot be compressed, pushing fluid through a pipe is just like pushing a steel bar through a pipe. Unlike a steel bar, however, fluid can be directed through many twists and turns on its way to its destination, arriving with the exact same motion and pressure that it started with. It is very important that the fluid is pure liquid and that there are no air bubbles in it. Air can compress, which causes a sponginess to the pedal and severely reduced braking efficiency. If air is suspected, then the system must be bled to remove the air. There are “bleeder screws” at each wheel cylinder and caliper for this purpose.

On a disk brake, the fluid from the master cylinder is forced into a caliper where it presses against a piston. The piston, in-turn, squeezes two brake pads against the disk (rotor), which is attached to the wheel, forcing it to slow down or stop.

This process is similar to a bicycle brake where two rubber pads rub against the wheel rim creating friction.

With drum brakes, fluid is forced into the wheel cylinder, which pushes the brake shoes out so that the friction linings are pressed against the drum, which is attached to the wheel, causing the wheel to stop.

In either case, the friction surfaces of the pads on a disk brake system, or the shoes on a drum brake convert the forward motion of the vehicle into heat. Heat is what causes the friction surfaces (linings) of the pads and shoes to eventually wear out and require replacement.

Let’s take a closer look at each of the components in a brake system and see where other problems can occur…

Master Cylinder

The master cylinder is located in the engine compartment on the firewall, directly in front of the driver’s seat. A typical master cylinder is actually two completely separate master cylinders in one housing, each handling two wheels. This way if one side fails, you will still be able to stop the car. The brake warning light on the dash will light if either side fails, alerting you to the problem. Master cylinders have become very reliable and rarely malfunction; however, the most common problem that they experience is an internal leak. This will cause the brake pedal to slowly sink to the floor when your foot applies steady pressure. Letting go of the pedal and immediately stepping on it again brings the pedal back to normal height.

Brake Fluid

Brake fluid is a special oil that has specific properties. It is designed to withstand cold temperatures without thickening as well as very high temperatures without boiling. (If the brake fluid should boil, it will cause you to have a spongy pedal and the car will be hard to stop.) Brake fluid must meet standards that are set by the Department of Transportation (DOT). The current standard is DOT-3, which has a boiling point of 460: F. But check your owners manual to see what your vehicle manufacturer recommends.

The brake fluid reservoir is on top of the master cylinder. Most cars today have a transparent reservoir so that you can see the level without opening the cover. The brake fluid level will drop slightly as the brake pads wear. This is a normal condition and no cause for concern. If the level drops noticeably over a short period of time or goes down to about two thirds full, have your brakes checked as soon as possible. Keep the reservoir covered except for the amount of time you need to fill it and never leave a can of brake fluid uncovered. Brake fluid must maintain a high boiling point. Exposure to air will cause the fluid to absorb moisture, which will lower that boiling point.
NEVER PUT ANYTHING BUT APPROVED BRAKE FLUID IN YOUR BRAKES. ANYTHING ELSE CAN CAUSE SUDDEN BRAKE FAILURE! Any other type of oil or other fluid will react with the brake fluid and very quickly destroy the rubber seals in the brake system causing brake failure.

Brake Lines

The brake fluid travels from the master cylinder to the wheels through a series of steel tubes and reinforced rubber hoses. Rubber hoses are used only in places that require flexibility, such as at the front wheels, which move up and down as well as steer. The rest of the system uses non-corrosive seamless steel tubing with special fittings at all attachment points. If a steel line requires a repair, the best procedure is to replace the complete line. If this is not practical, a line can be repaired using special splice fittings that are made for brake system repair. You must never use brass “compression” fittings or copper tubing to repair a brake system. They are dangerous and illegal.

Other Components in the Hydraulic System

Proportioning valve or Equalizer Valve
These valves are mounted between the master cylinder and the rear wheels. They are designed to adjust the pressure between the front and rear brakes depending on how hard you are stopping. The shorter you stop, the more of the vehicle’s weight is transferred to the front wheels, in some cases, causing the rear to lift and the front to dive. These valves are designed to direct more pressure to the front and less pressure to the rear the harder you stop. This minimizes the chance of premature lockup at the rear wheels.

Pressure Differential Valve
This valve is usually mounted just below the master cylinder and is responsible for turning the brake warning light on when it detects a malfunction. It measures the pressure from the two sections of the master cylinder and compares them. Since it is mounted ahead of the proportioning or equalizer valve, the two pressures it detects should be equal. If it detects a difference, it means that there is probably a brake fluid leak somewhere in the system.

Combination Valve
The Combination valve is simply a proportioning valve and a pressure differential valve that is combined into one unit.

Electronic Brake Force Distribution
Newer cars use the antilock brake hardware and the onboard computer to replace these proportioning valve systems with a system called Electronic Brake force Distribution (EBD) in order to distribute the exact amount of pressure at each wheel to insure a balanced brake system.

Disk Brakes

The disk brake is the best brake we have found so far. Disk brakes are used to stop everything from cars to locomotives and jumbo jets. Disk brakes wear longer, are less affected by water, are self adjusting, self cleaning, less prone to grabbing or pulling and stop better than any other system around. The main components of a disk brake are the Brake Pads, Rotor, Caliper and Caliper Support.

Brake Pads
There are two brake pads on each caliper. They are constructed of a metal “shoe” with the lining riveted or bonded to it. The pads are mounted in the caliper, one on each side of the rotor. Brake linings used to be made primarily of asbestos because of its heat absorbing properties and quiet operation; however, due to health risks, asbestos has been outlawed, so new materials are now being used. Brake pads wear out with use and must be replaced periodically. There are many types and qualities of pads available. The differences have to do with brake life (how long the new pads will last) and noise (how quiet they are when you step on the brake). Harder linings tend to last longer and stop better under heavy use but they may produce an irritating squeal when they are applied. Technicians that work on brakes usually have a favorite pad that gives a good compromise that their customers can live with.

Brake pads should be checked for wear periodically. If the lining wears down to the metal brake shoe, then you will have a “Metal-to-Metal” condition where the shoe rubs directly against the rotor causing severe damage and loss of braking efficiency. Some brake pads come with a “brake warning sensor” that will emit a squealing noise when the pads are worn to a point where they should be changed. This noise will usually be heard when your foot is off the brake and disappear when you step on the brake. If you hear this noise, have your brakes checked as soon as possible.

Rotor
The disk rotor is made of iron with highly machined surfaces where the brake pads contact it. Just as the brake pads wear out over time, the rotor also undergoes some wear, usually in the form of ridges and groves where the brake pad rubs against it. This wear pattern exactly matches the wear pattern of the pads as they seat themselves to the rotor. When the pads are replaced, the rotor must be machined smooth to allow the new pads to have an even contact surface to work with. Only a small amount of material can be machined off of a rotor before it becomes unusable and must be replaced. A minimum thickness measurement is stamped on every rotor and the technician doing the brake job will measure the rotor before and after machining it to make sure it doesn’t go below the legal minimum. If a rotor is cut below the minimum, it will not be able to handle the high heat that brakes normally generate. This will cause the brakes to “fade,” greatly reducing their effectiveness to a point where you may not be able to stop!

Caliper & Support
There are two main types of calipers: Floating calipers and fixed calipers. There are other configurations but these are the most popular. Calipers must be rebuilt or replaced if they show signs of leaking brake fluid.

Single Piston Floating Calipers are the most popular and also least costly to manufacture and service. A floating caliper “floats” or moves in a track in its support so that it can center itself over the rotor. As you apply brake pressure, the hydraulic fluid pushes in two directions. It forces the piston against the inner pad, which in turn pushes against the rotor. It also pushes the caliper in the opposite direction against the outer pad, pressing it against the other side of the rotor. Floating calipers are also available on some vehicles with two pistons mounted on the same side. Two piston floating calipers are found on more expensive cars and can provide an improved braking “feel”.

Four Piston Fixed Calipers are mounted rigidly to the support and are not allowed to move. Instead, there are two pistons on each side that press the pads against the rotor. Four piston calipers have a better feel and are more efficient, but are more expensive to produce and cost more to service. This type of caliper is usually found on more expensive luxury and high performance cars.

Drum Brakes

So if disk brakes are so great, how come we still have cars with drum brakes? The reason is cost. While all vehicles produced for many years have disk brakes on the front, drum brakes are cheaper to produce for the rear wheels. The main reason is the parking brake system. On drum brakes, adding a parking brake is the simple addition of a lever, while on disk brakes, we need a complete mechanism, in some cases, a complete mechanical drum brake assembly inside the disk brake rotor! Parking brakes must be a separate system that does not use hydraulics. It must be totally mechanical, but more on parking brakes later.

Drum brakes consist of a backing plate, brake shoes, brake drum, wheel cylinder, return springs and an automatic or self-adjusting system. When you apply the brakes, brake fluid is forced under pressure into the wheel cylinder, which in turn pushes the brake shoes into contact with the machined surface on the inside of the drum. When the pressure is released, return springs pull the shoes back to their rest position. As the brake linings wear, the shoes must travel a greater distance to reach the drum. When the distance reaches a certain point, a self-adjusting mechanism automatically reacts by adjusting the rest position of the shoes so that they are closer to the drum.

Brake Shoes
Like the disk pads, brake shoes consist of a steel shoe with the friction material or lining riveted or bonded to it. Also like disk pads, the linings eventually wear out and must be replaced. If the linings are allowed to wear through to the bare metal shoe, they will cause severe damage to the brake drum.

Backing Plate
The backing plate is what holds everything together. It attaches to the axle and forms a solid surface for the wheel cylinder, brake shoes and assorted hardware. It rarely causes any problems.

Brake Drum
Brake drums are made of iron and have a machined surface on the inside where the shoes make contact. Just as with disk rotors, brake drums will show signs of wear as the brake linings seat themselves against the machined surface of the drum. When new shoes are installed, the brake drum should be machined smooth. Brake drums have a maximum diameter specification that is stamped on the outside of the drum. When a drum is machined, it must never exceed that measurement. If the surface cannot be machined within that limit, the drum must be replaced.

Wheel Cylinder
The wheel cylinder consists of a cylinder that has two pistons, one on each side. Each piston has a rubber seal and a shaft that connects the piston with a brake shoe. When brake pressure is applied, the pistons are forced out pushing the shoes into contact with the drum. Wheel cylinders must be rebuilt or replaced if they show signs of leaking.

Return Springs
Return springs pull the brake shoes back to their rest position after the pressure is released from the wheel cylinder. If the springs are weak and do not return the shoes all the way, it will cause premature lining wear because the linings will remain in contact with the drum. A good technician will examine the springs during a brake job and recommend their replacement if they show signs of fatigue. On certain vehicles, the technician may recommend replacing them even if they look good as inexpensive insurance.

Self Adjusting System
The parts of a self adjusting system should be clean and move freely to insure that the brakes maintain their adjustment over the life of the linings. If the self adjusters stop working, you will notice that you will have to step down further and further on the brake pedal before you feel the brakes begin to engage. Disk brakes are self adjusting by nature and do not require any type of mechanism. When a technician performs a brake job, aside from checking the return springs, he will also clean and lubricate the self adjusting parts where necessary.

Parking Brakes

The parking brake (a.k.a. emergency brake) system controls the rear brakes through a series of steel cables that are connected to either a hand lever or a foot pedal. The idea is that the system is fully mechanical and completely bypasses the hydraulic system so that the vehicle can be brought to a stop even if there is a total brake failure.
On drum brakes, the cable pulls on a lever mounted in the rear brake and is directly connected to the brake shoes. this has the effect of bypassing the wheel cylinder and controlling the brakes directly.
Disk brakes on the rear wheels add additional complication for parking brake systems. There are two main designs for adding a mechanical parking brake to rear disk brakes. The first type uses the existing rear wheel caliper and adds a lever attached to a mechanical corkscrew device inside the caliper piston. When the parking brake cable pulls on the lever, this corkscrew device pushes the piston against the pads, thereby bypassing the hydraulic system, to stop the vehicle. This type of system is primarily used with single piston floating calipers, if the caliper is of the four piston fixed type, then that type of system can’t be used. The other system uses a complete mechanical drum brake unit mounted inside the rear rotor. The brake shoes on this system are connected to a lever that is pulled by the parking brake cable to activate the brakes. The brake “drum” is actually the inside part of the rear brake rotor.

On cars with automatic transmissions, the parking brake is rarely used. This can cause a couple of problems. The biggest problem is that the brake cables tend to get corroded and eventually seize up causing the parking brake to become inoperative. By using the parking brake from time to time, the cables stay clean and functional. Another problem comes from the fact that the self adjusting mechanism on certain brake systems uses the parking brake actuation to adjust the brakes. If the parking brake is never used, then the brakes never get adjusted.

Power Brake Booster

The power brake booster is mounted on the firewall directly behind the master cylinder and, along with the master cylinder, is directly connected with the brake pedal. Its purpose is to amplify the available foot pressure applied to the brake pedal so that the amount of foot pressure required to stop even the largest vehicle is minimal. Power for the booster comes from engine vacuum. The automobile engine produces vacuum as a by-product of normal operation and is freely available for use in powering accessories such as the power brake booster. Vacuum enters the booster through a check valve on the booster. The check valve is connected to the engine with a rubber hose and acts as a one-way valve that allows vacuum to enter the booster but does not let it escape. The booster is an empty shell that is divided into two chambers by a rubber diaphragm. There is a valve in the diaphragm that remains open while your foot is off the brake pedal so that vacuum is allowed to fill both chambers. When you step on the brake pedal, the valve in the diaphragm closes, separating the two chambers and another valve opens to allow air in the chamber on the brake pedal side. This is what provides the power assist. Power boosters are very reliable and cause few problems of their own, however, other things can contribute to a loss of power assist. In order to have power assist, the engine must be running. If the engine stalls or shuts off while you are driving, you will have a small reserve of power assist for two or three pedal applications but, after that, the brakes will be extremely hard to apply and you must put as much pressure as you can to bring the vehicle to a stop.

Anti-Lock Brakes (ABS)

The most efficient braking pressure takes place just before each wheel locks up. When you slam on the brakes in a panic stop and the wheels lock up, causing a screeching sound and leaving strips of rubber on the pavement, you do not stop the vehicle nearly as short as it is capable of stopping. Also, while the wheels are locked up, you loose all steering control so that, if you have an opportunity to steer around the obstacle, you will not be able to do so. Another problem occurs during an extended skid is that you will burn a patch of rubber off the tire, which causes a “flat spot” on the tread that will produce an annoying thumping sound as you drive.

Anti-lock brake systems solve this lockup problem by rapidly pumping the brakes whenever the system detects a wheel that is locked up. In most cases, only the wheel that is locked will be pumped, while full braking pressure stays available to the other wheels. This effect allows you to stop in the shortest amount of time while maintaining full steering control even if one or more wheels are on ice. The system uses a computer to monitor the speed of each wheel. When it detects that one or more wheels have stopped or are turning much slower than the remaining wheels, the computer sends a signal to momentarily remove and reapply or pulse the pressure to the affected wheels to allow them to continue turning. This “pumping” of the brakes occurs at ten or more times a second, far faster then a human can pump the brakes manually. If you step on the brakes hard enough to engage the anti-lock system, you may feel a strong vibration in the brake pedal. This is a normal condition and indicates that the system is working, however, it can be disconcerting to some people who don’t expect it. If your vehicle has anti-lock brakes, read your owner’s manual to find out more about it.

The system consists of an electronic control unit, a hydraulic actuator, and wheel speed sensors at each wheel. If the control unit detects a malfunction in the system, it will illuminate an ABS warning light on the dash to let you know that there is a problem. If there is a problem, the anti-lock system will not function but the brakes will otherwise function normally.

All-Makes is the place to go for all your auto repair needs in Rio Rancho, NM.

Dashboard Gauges

The minimum number of gauges on a passenger car dashboard is the speedometer and the fuel gauge. The most common additional gauge is the temperature gauge followed by the tachometer, voltmeter and oil pressure gauge. If your car does not have a temperature gauge, oil pressure gauge or charging system gauge, then you will have a warning light for these functions.

The most common configuration in today’s family car is: Speedometer, Tachometer, Fuel & Temperature.

Typical instrument panel

Note: To find out more about the gauges on your car, the best source of information is your owner’s manual.

• Speedometer
  In the past, the most used of the gauges. The speedometer was usually driven by a cable that spins inside a flexible tube.  The cable is connected on one side to the speedometer, and on the other side to the speedometer gear inside the transmission.  Today, just about all vehicles have eliminated the cable and use an electronic sensor to measure wheel speed and send the signal to an electronically driven speedometer.

The accuracy of the speedometer can be affected by the size of the tires. If the tires are larger in diameter than original equipment, the speedometer will read that you are going slower then you actually are.  On older vehicles, another cause for inaccurate speed readings was an improper speedometer gear inside the transmission. This can sometimes happen after a replacement transmission has been installed.  Most good transmission shops are aware of this and will make sure that the correct speedometer gear is in the new transmission.

On vehicles with electronic speedometers, the computer has settings to for speedometer calibration when necessary, to allow a technician to adjust for different sized tires. These calibrations usually require specialized equipment like diagnostic scanners to do these types of adjustments.

• Fuel Gauge

Deliberately designed to be inaccurate! After you fill up the tank, the gauge will stay on full for a long time, then slowly drop until it reads 3/4 full. After that, it moves progressively faster until the last quarter of a tank seems to go very quickly. This is a bit of psychological slight-of-hand to give the impression that the car gets better gas mileage than it does, it seems to reduce the number of complaints from new car buyers during the first few weeks after they bought the car.
The fuel gauge shown here is probably more accurate than most. Notice the difference between 3/4 to full and empty to 1/4.
When the needle drops below E, there is usually 1 or 2 gallons left in reserve. To find out for sure, pull out your owner’s manual and find out how many gallons of gas your tank holds, then the next time you fill up an empty tank, check how many gallons it took to fill it. The difference is your reserve.
Note: It is not a good idea to let your tank drop below 1/4.  This is because your fuel pump is submerged in fuel at the bottom of the tank.  The liquid fuel helps to keep the fuel pump cool.  If the fuel level goes too low and uncovers the pump, the pump will run hotter than normal.  If you do this often enough, it can shorten the life of the fuel pump and eventually cause it to fail.

• Temperature Gauge or warning lamp
  This gauge measures the temperature of the engine coolant in degrees. When you first start the car, the gauge will read cold. If you turn the heater on when the engine is cold, it will blow cold air. When the gauge starts moving away from cold, you can then turn the heater on and get warm air. Most temperature gauges do not show degrees like the one pictured here. Instead they will read cold, hot, and have a normal range as pictured in the dash panel at the top of this page.

It is very important to monitor the temperature gauge to be sure that your engine is not overheating. If you notice that the gauge is reading much hotter than it usually is and the outside temperature is not unusually hot, have the cooling system checked as soon as possible. Note: If the temperature gauge moves all the way to hot, or if the temperature warning light comes on, the engine is overheating! Safely pull off the road and turn the engine off and let it cool. An overheating engine can quickly cause serious engine damage!

• Tachometer
  The tachometer measures how fast the engine is turning in RPM (Revolutions Per Minute). This information is useful if your car has a standard shift transmission and you want to shift at the optimum RPM for best fuel economy or best acceleration. One of the least used gauges on a car with an automatic transmission. You should never race your engine so fast that the tach moves into the red zone as this can cause engine damage. Some engines are protected by the engine computer from going into the red zone.  Usually, the tachometer shows single digit markings like 1, 2, 3 etc. Somewhere, you will also see an indicator that says RPM x 1000.  This means that you multiply the reading by 1000 to get the actual RPM, so if the needle is pointing to 2, the engine is running at 2000 RPM.
• Oil Pressure Gauge or warning lamp
  Measures engine oil pressure in pounds per square inch. Oil pressure is just as important to an engine as blood pressure is to a person. If you run an engine with no oil pressure even for less than a minute, you can easily destroy it. Most cars have an oil lamp that lights when oil pressure is dangerously low. If it comes on while you’re driving, stop the vehicle as soon as is safely possible and shut off the engine. Then, check the oil level and add oil as necessary.
• Charging system gauge or warning lamp
  The charging system is what provides the electrical current for your vehicle. Without a charging system, your battery will soon be depleted and your vehicle will shut down. The charging system gauge or warning lamp monitors the health of this system so that you have a warning of a problem before you get stuck.
  When a charging problem is indicated, you can still drive a short distance to find help unlike an oil pressure or coolant temperature problem which can cause serious engine damage if you continue to drive. The worst that can happen is that you get stuck in a bad location.
  A charging system warning lamp is a poor indicator of problems in that there are many charging problems that it will not recognize. If it does light while you are driving, it usually means the charging system is not working at all. The most common cause is a broken alternator belt.
  There are two types of gauges used to monitor charging systems: a voltmeter which measures system voltage and an ammeter which measures amperage going out of, or coming into the battery. Most modern cars that have gauges use a voltmeter because it is a much better indicator of charging system health. A voltmeter is usually the first tool a technician uses when checking out a charging system

A modern automobile has a 12 volt electrical system. A fully charged battery will read about 12.5 volts when the engine is not running. When the engine is running, the charging system takes over so that the voltmeter will read 14 to 14.5 volts and should stay there unless there is a heavy load on the electrical system such as wipers, lights, heater and rear defogger all operating together while the engine is idling at which time the voltage may drop. If the voltage drops below 12.5, it means that the battery is providing some of the current. You may notice that your dash lights dim at this point. If this happens for an extended period, the battery will run down and may not have enough of a charge to start the car after shutting it off. This should never happen with a healthy charging system because as soon as you step on the gas, the charging system will recharge the battery. If the voltage is constantly below 14 volts, you should have the system checked. If the voltage ever goes above 15 volts, there is a problem with the voltage regulator. Have the system checked as soon as possible as this “overcharging” condition can cause damage to your electrical system.

If you think of electricity as water, voltage is like water pressure, whereas amperage is like the volume of water. If you increase pressure, then more water will flow through a given size pipe, but if you increase the size of the pipe, more water will flow at a lower pressure. An ammeter will read from negative amperage when the battery is providing most of the current thereby depleting itself, to positive amperage if most of the current is coming from the charging system. If the battery is fully charged and there is minimal electrical demand, then the ammeter should read close to zero, but should always be on the positive side of zero. It is normal for the ammeter to read high positive amperage in order to recharge the battery after starting, but it should taper off in a few minutes. If it continues to read more than 10 or 20 amps even though the lights, wipers and other electrical devices are turned off, you may have a weak battery and should have it checked.

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All-Makes is the place to go for all your auto repair needs in Rio Rancho, NM.

Ignition System

The purpose of the ignition system is to create a spark that will ignite the fuel-air mixture in the cylinder of an engine.  It must do this at exactly the right instant and do it at the rate of up to several thousand times per minute for each cylinder in the engine.  If the timing of that spark is off by a small fraction of a second, the engine will run poorly or not run at all.

The ignition system sends an extremely high voltage to the spark plug in each cylinder when the piston is at the top of its compression stroke.  The tip of each spark plug contains a gap that the voltage must jump across in order to reach ground.  That is where the spark occurs.

The voltage that is available to the spark plug is somewhere between 20,000 volts and 50,000 volts or better.  The job of the ignition system is to produce that high voltage from a 12 volt source and get it to each cylinder in a specific order, at exactly the right time.

Let’s see how this is done.

The ignition system has two tasks to perform.  First, it must create a voltage high enough (20,000+) to arc across the gap of a spark plug, thus creating a spark strong enough to ignite the air/fuel mixture for combustion.  Second, it must control the timing of that the spark so it occurs at the exact right time and send it to the correct cylinder.

The ignition system is divided into two sections, the primary circuit and the secondary circuit.  The low voltage primary circuit operates at battery voltage (12 to 14.5 volts) and is responsible for generating the signal to fire the spark plug at the exact right time and sending that signal to the ignition coil.  The ignition coil is the component that converts the 12 volt signal into the high 20,000+ volt charge.  Once the voltage is stepped up, it goes to the secondary circuit which then directs the charge to the correct spark plug at the right time.

The Basics
Before we begin this discussion, let’s talk a bit about electricity in general.  I know that this is basic stuff, but there was a time that you didn’t know about this and there are people who need to know the basics so that they could make sense of what follows.

All automobiles work on DC, or Direct Current.   This means that current moves in one direction, from the positive battery terminal to the negative battery terminal.  In the case of the automobile, the negative battery terminal is connected by a heavy cable directly to the body and the engine block of the vehicle.  The body and any metal component in contact with it is called the Ground.  This means that a circuit that needs to send current back to the negative side of the battery can be connected to any part of the vehicle’s metal body or the metal engine block.

A good example to see how this works is the headlight circuit.  The headlight circuit consists of a wire that goes from the positive battery terminal to the headlight switch.  Another wire goes from the headlight switch to one of two terminals on the headlamp bulb.  Finally, a third wire goes from a second terminal on the bulb to the metal body of the car.  When you switch the headlights on, you are connecting the wire from the battery with the wire to the headlamps allowing battery current to go directly to the headlamp bulbs.  Electricity passes through the filaments inside the bulb, then out the other wire to the metal body.  From there, the current goes back to the negative terminal of the battery completing the circuit.  Once the current is flowing through this circuit, the filament inside the headlamp gets hot and glows brightly.  Let there be light.

Now, back to the ignition system.  The basic principle of the electrical spark ignition system has not changed for over 75 years. What has changed is the method by which the spark is created and how it is distributed.

Currently, there are three distinct types of ignition systems,  The Mechanical Ignition System was used prior to 1975.  It was mechanical and electrical and used no electronics.  By understanding these early systems, it will be easier to understand the new electronic and computer controlled ignition systems, so don’t skip over it.  The Electronic Ignition System started finding its way to production vehicles during the early ’70s and became popular when better control and improved reliability became important with the advent of emission controls.  Finally, the Distributorless Ignition System became available in the mid ’80s.  This system was always computer controlled and contained no moving parts, so reliability was greatly improved.  Most of these systems required no maintenance except replacing the spark plugs at intervals from 60,000 to over 100,000 miles.

Let’s take a detailed look at each system and see how they work.
The Mechanical Ignition System
(from the dawn of the automobile to 1974)

The distributor is the nerve center of the mechanical ignition system and has two tasks to perform.  First, it is responsible for triggering the ignition coil to generate a spark at the precise instant that it is required (which varies depending how fast the engine is turning and how much load it is under).  Second, the distributor is responsible for directing that spark to the proper cylinder (which is why it is called a distributor)

The circuit that powers the ignition system is simple and straight forward. (see above)  When you insert the key in the ignition switch and turn the key to the Run position, you are sending current from the battery through a wire directly to the positive (+) side of the ignition coil.  Inside the coil is a series of copper windings that loop around the coil over a hundred times before exiting out the negative (-) side of the coil.  From there, a wire takes this current over to the distributor and is connected  to a special on/off switch, called the points.  When the points are closed, this current goes directly to ground.  When current flows from the ignition switch, through the windings in the coil, then to ground, it builds a strong magnetic field inside the coil.

The points are made up of a fixed contact point that is fastened to a plate inside the distributor, and a movable contact point mounted on the end of a spring loaded arm.. The movable point rides on a 4,6, or 8 lobe cam (depending on the number of cylinders in the engine) that is mounted on a rotating shaft inside the distributor.  This distributor cam rotates in time with the engine, making one complete revolution for every two revolutions of the engine.  As it rotates, the cam pushes the points open and closed.  Every time the points open, the flow of current is interrupted through the coil, thereby collapsing the magnetic field and releasing a high voltage surge through the secondary coil windings.  This voltage surge goes out the top of the coil and through the high-tension coil wire.

Now, we have the voltage necessary to fire the spark plug, but we still have to get it to the correct cylinder.  The coil wire goes from the coil directly to the center of the distributor cap.  Under the cap is a rotor that is mounted on top of the rotating shaft.  The rotor has a metal strip on the top that is in constant contact with the center terminal of the distributor cap.  It receives the high voltage surge from the coil wire and sends it to the other end of the rotor which rotates past each spark plug terminal inside the cap.  As the rotor turns on the shaft, it sends the voltage to the correct spark plug wire, which in turn sends it to the spark plug.  The voltage enters the spark plug at the terminal at the top and travels down the core until it reaches the tip.  It then jumps across the gap at the tip of the spark plug, creating a spark suitable to ignite the fuel-air mixture inside that cylinder.

The description I just provided is the simplified version, but should be helpful to visualize the process, but we left out a few things that make up this type of ignition system.  For instance, we didn’t talk about the condenser that is connected to the points, nor did we talk about the system to advance the timing.  Let’s take a look at each section and explore it in more detail.

The ignition switch
There are two separate circuits that go from the ignition switch to the coil.  One circuit runs through a resistor in order to step down the voltage about 15% in order to protect the points from premature wear.  The other circuit sends full battery voltage to the coil.  The only time this circuit is used is during cranking.  Since the starter draws a considerable amount of current to crank the engine, additional voltage is needed to power the coil.  So when the key is turned to the spring-loaded start position, full battery voltage is used.  As soon as the engine is running, the driver releases the key to the run position which directs current through the primary resistor to the coil.

On some vehicles, the primary resistor is mounted on the firewall and is easy to replace if it fails.  On other vehicles, most notably vehicles manufactured by GM, the primary resistor is a special resistor wire and is bundled in the wiring harness with other wires, making it more difficult to replace, but also more durable.

The Distributor
When you remove the distributor cap from the top of the distributor, you will see the points and condenser.  The condenser is a simple capacitor that can store a small amount of current.  When the points begin to open, the current flowing through the points looks for an alternative path to ground.  If the condenser were not there, it would try to jump across the gap of the points as they begin to open.  If this were allowed to happen, the points would quickly burn up and you would hear heavy static on the car radio.  To prevent this, the condenser acts like a path to ground. It really is not, but by the time the condenser is saturated, the points are too far apart for the small amount of voltage to jump across the wide point gap.  Since the arcing across the opening points is eliminated, the points last longer and there is no static on the radio from point arcing.

The points require periodic adjustments in order to keep the engine running at peek efficiency.  This is because there is a rubbing block on the points that is in contact with the cam and this rubbing block wears out over time changing the point gap.  There are two ways that the points can be measured to see if they need an adjustment.  One way is by measuring the gap between the open points when the rubbing block is on the high point of the cam.  The other way is by measuring the dwell electrically.  The dwell is the amount, in degrees of cam rotation, that the points stay closed.

On some vehicles, points are adjusted with the engine off and the distributor cap removed.  A mechanic will loosen the fixed point and move it slightly, then retighten it in the correct position using a feeler gauge to measure the gap.  On other vehicles, most notably GM cars, there is a window in the distributor where a mechanic can insert a tool and adjust the points using a dwell meter while the engine is running.  Measuring dwell is much more accurate than setting the points with a feeler gauge.

Points have a life expectancy of about 10,000 miles at which time they have to be replaced. This is done during a routine major tune up.  During the tune up, points, condenser, and the spark plugs are replaced, the timing is set and the carburetor is adjusted.  In some cases, to keep the engine running efficiently, a minor tune up would be performed at 5,000 mile increments to adjust the points and reset the timing.

Ignition Coil
The ignition coil is nothing more that an electrical transformer.  It contains both primary and secondary winding circuits. The coil primary winding contains 100 to 150 turns of heavy copper wire. This wire must be insulated so that the voltage does not jump from loop to loop, shorting it out.  If this happened, it could not create the primary magnetic field that is required. The primary circuit wire goes into the coil through the positive terminal, loops around the primary windings, then exits through the negative terminal.

The coil secondary winding circuit contains 15,000 to 30,000 turns of fine copper wire, which also must be insulated from each other.  The secondary windings sit inside the loops of the primary windings.  To further increase the coils magnetic field the windings are wrapped around a soft iron core. To withstand the heat of the current flow, the coil is filled with oil which helps keep it cool.

The ignition coil is the heart of the ignition system. As current flows through the coil a strong magnetic field is built up. When the current is shut off, the collapse of this magnetic field to the secondary windings induces a high voltage which is released through the large center terminal.  This voltage is then directed to the spark plugs through the distributor.

Ignition Timing
The timing is set by loosening a hold-down screw and rotating the body of the distributor.  Since the spark is triggered at the exact instant that the points begin to open, rotating the distributor body (which the points are mounted on) will change the relationship between the position of the points and the position of the distributor cam, which is on the shaft that is geared to the engine rotation.

While setting the initial, or base timing is important, for an engine to run properly, the timing needs to change depending on the speed of the engine and the load that it is under.  If we can move the plate that the points are mounted on, or we could change the position of the distributor cam in relation to the gear that drives it, we can alter the timing dynamically to suit the needs of the engine.

Why do we need the timing to advance when the engine runs faster?
When the spark plug fires in the combustion chamber, it ignites whatever fuel and air mixture is present at the tip of the spark plug.  The fuel that surrounds the tip is ignited by the burning that was started by the spark plug, not by the spark itself.  That flame front continues to expand outward at a specific speed that is always the same, regardless of engine speed.  It does not begin to push the piston down until it fills the combustion chamber and has no where else to go.  In order to maximize the amount of power generated, the spark plug must fire before the piston reaches the top of the cylinder so that the burning fuel is ready to push the piston down as soon as it is at the top of its travel.  The faster the engine is spinning, the earlier we have to fire the plug to produce maximum power.

There are two mechanisms that allow the timing to change: Centrifugal Advance and Vacuum Advance.

Centrifugal Advance changes the timing in relation to the speed (RPM) of the engine.  It uses a pair of weights that are connected to the spinning distributor shaft.  These weights are hinged on one side to the lower part of the shaft and connected by a linkage to the upper shaft where the distributor cam is.  The weights are held close to the shaft be a pair of springs.  As the shaft spins faster, the weights are pulled out by centrifugal force against the spring pressure.  The faster the shaft spins, the more they are pulled out.  When the weights move out, it changes the alignment between the lower and upper shaft, causing the timing to advance.

Vacuum Advance works by changing the position of the points in relationship to the distributor body.  An engine produces vacuum while it is running with the throttle closed.  In other words, your foot is off the gas pedal.  In this configuration, there is very little fuel and air in the combustion chamber.

Vacuum advance uses a vacuum diaphragm connected to a link that can move the plate that the points are mounted on.  By sending engine vacuum to the vacuum advance diaphragm, timing is advanced.  On older cars, the vacuum that is used is port vacuum, which is just above the throttle plate.  With this setup, there is no vacuum present at the vacuum advance diaphragm while the throttle is closed.  When the throttle is cracked opened, vacuum is sent to the vacuum advance, advancing the timing.

On early emission controlled vehicles, manifold vacuum was used so that vacuum was present at the vacuum advance at idle in order to provide a longer burn time for the lean fuel mixtures on those engines.  When the throttle was opened, vacuum was reduced causing the timing to retard slightly.  This was necessary because as the throttle opened, more fuel was added to the mixture reducing the need for excessive advance.  Many of these early emission controlled cars had a vacuum advance with electrical components built into the advance unit to modify the timing under certain conditions.

Both Vacuum and Centrifugal advance systems worked together to extract the maximum efficiency from the engine.  If either system was not functioning properly, both performance and fuel economy would suffer.  Once computer controls were able to directly control the engine’s timing, vacuum and centrifugal advance mechanisms were no longer necessary and were eliminated.

Ignition Wires
These cables are designed to handle 20,000 to more than 50,000 volts, enough voltage to toss you across the room if you were to be exposed to it.  The job of the spark plug wires is to get that enormous power to the spark plug without leaking out.  Spark plug wires have to endure the heat of a running engine as well as the extreme changes in the weather.  In order to do their job, spark plug wires are fairly thick, with most of that thickness devoted to insulation with a very thin conductor running down the center.  Eventually, the insulation will succumb to the elements and the heat of the engine and begins to harden, crack, dry out, or otherwise break down. When that happens, they will not be able to deliver the necessary voltage to the spark plug and a misfire will occur.  That is what is meant by “Not running on all cylinders”.  To correct this problem, the spark plug wires would have to be replaced.

Spark plug wires are routed around the engine very carefully.  Plastic clips are often used to keep the wires separated so that they do not touch together.  This is not always necessary, especially when the wires are new, but as they age, they can begin to leak and crossfire on damp days causing hard starting or a rough running engine.

Spark plug wires go from the distributor cap to the spark plugs in a very specific order.  This is called the “firing order” and is part of the engine design.  Each spark plug must only fire at the end of the compression stroke.  Each cylinder has a compression stroke at a different time, so it is important for the individual spark plug wire to be routed to the correct cylinder.

For instance, a popular V8 engine firing order is 1, 8, 4, 3, 6, 5, 7, 2.  The cylinders are numbered from the front to the rear with cylinder #1 on the front-left of the engine.  So the cylinders on the left side of the engine are numbered 1, 3, 5, 7 while the right side are numbered 2, 4, 6, 8.  On some engines, the right bank is 1, 2, 3, 4 while the left bank is 5, 6, 7, 8.  A repair manual will tell you the correct firing order and cylinder layout for a particular engine.

The next thing we need to know is what direction the distributor is rotating in, clockwise or counter-clockwise, and which terminal on the distributor cap that #1 cylinder is located.  Once we have this information, we can begin routing the spark plug wires.

If the wires are installed incorrectly, the engine may backfire, or at the very least, not run on all cylinders.  It is very important that the wires are installed correctly.

Spark Plugs
The ignition system’s sole reason for being is to service the spark plug.  It must provide sufficient voltage to jump the gap at the tip of the spark plug and do it at the exact right time, reliably on the order of thousands of times per minute for each spark plug in the engine.

The modern spark plug is designed to last many thousands of miles before it requires replacement.  These electrical wonders come in many configurations and heat ranges to work properly in a given engine.

The heat range of a spark plug dictates whether it will be hot enough to burn off any residue that collects on the tip, but not so hot that it will cause pre-ignition in the engine.  Pre-ignition is caused when a spark plug is so hot, that it begins to glow and ignite the fuel-air mixture prematurely, before the spark.  Most spark plugs contain a resistor to suppress radio interference.  The gap on a spark plug is also important and must be set before the spark plug is installed in the engine.  If the gap is too wide, there may not be enough voltage to jump the gap, causing a misfire.  If the gap is too small, the spark may be inadequate to ignite a lean fuel-air mixture, also causing a misfire.

The Electronic Ignition System
(from 1970′s to today)

This section will describe the main differences between the early point & condenser systems and the newer electronic systems.  If you are not familiar with the way an ignition system works in general, I strongly recommend that you first read the previous section The Mechanical Ignition System.

In the electronic ignition system, the points and condenser were replaced by electronics.  On these systems, there were several methods used to replace the points and condenser in order to trigger the coil to fire.  One method used a metal wheel with teeth, usually one for each cylinder.  This is called an armature or reluctor.  A magnetic pickup coil senses when a tooth passes and sends a signal to the control module to fire the coil.

Other systems used an electric eye with a shutter wheel to send a signal to the electronics that it was time to trigger the coil to fire.  These systems still need to have the initial timing adjusted by rotating the distributor housing.

The advantage of this system, aside from the fact that it is maintenance free, is that the control module can handle much higher primary voltage than the mechanical points.  Voltage can even be stepped up before sending it to the coil, so the coil can create a much hotter spark, on the order of 50,000 volts instead of 20,000 volts that is common with the mechanical systems.  These systems only have a single wire from the ignition switch to the coil since a primary resistor is no longer needed.

On some vehicles, this control module was mounted inside the distributor where the points used to be mounted.  On other designs, the control module was mounted outside the distributor with external wiring to connect it to the pickup coil.  On many General Motors engines, the control module was inside the distributor and the coil was mounted on top of the distributor for a one piece unitized ignition system.  GM called it High Energy Ignition or HEI for short.

The higher voltage that these systems provided allow the use of a much wider gap on the spark plugs for a longer, fatter spark.  This larger spark also allowed a leaner mixture for better fuel economy and still insure a smooth running engine.

The early electronic systems had limited or no computing power, so timing still had to be set manually and there was still a centrifugal and vacuum advance built into the distributor.

On some of the later systems, the inside of the distributor is empty and all triggering is performed by a sensor that watches a notched wheel connected to either the crankshaft or the camshaft.  These devices are called Crankshaft Position Sensor or Camshaft Position Sensor.  In these systems, the job of the distributor is solely to distribute the spark to the correct cylinder through the distributor cap and rotor.  The computer handles the timing and any timing advance necessary for the smooth running of the engine.

The Distributorless Ignition system
(from 1980′s to today)

Newer automobiles have evolved from a mechanical system (distributor) to a completely solid state electronic system with no moving parts.  These systems are completely controlled by the on-board computer.  In place of the distributor, there are multiple coils that each serve one or two spark plugs.  A typical 6 cylinder engine has 3 coils that are mounted together in a coil “pack”.  A spark plug wire comes out of each side of the individual coil and goes to the appropriate spark plug.  The coil fires both spark plugs at the same time.  One spark plug fires on the compression stroke igniting the fuel-air mixture to produce power, while the other spark plug fires on the exhaust stroke and does nothing.  On some vehicles, there is an individual coil for each cylinder mounted directly on top of the spark plug.  This design completely eliminates the high tension spark plug wires for even better reliability.  Most of these systems use spark plugs that are designed to last over 100,000 miles, which cuts down on maintenance costs.

This content is provided to you by All Makes Automotive Services.

All-Makes is the place to go for all your auto repair needs in Rio Rancho, NM.

Charging System

What is a Charging System?

The modern charging system hasn’t changed much in over 40 years.  It consists of the alternator, regulator (which is usually mounted inside the alternator) and the interconnecting wiring. The purpose of the charging system is to maintain the charge in the vehicle’s battery, and to provide the main source of electrical energy while the engine is running.

If the charging system stopped working, the battery’s charge would soon be depleted, leaving the car with a “dead battery.”   If the battery is weak and the alternator is not working, the engine may not have enough electrical current to fire the spark plugs, so the engine will stop running. If the battery is “dead”, it does not necessarily mean that there is anything wrong with it.  It is just depleted of its charge.  It can be brought back to life by recharging it with a battery charger, or by running the engine so that the alternator can charge it.

The main component in the charging system is the ALTERNATOR.  The alternator is a generator  that produces Alternating Current (AC), similar to the electrical current in your home.  This current is immediately converted to Direct Current (DC) inside the alternator.  This is because all modern automobiles have a 12 volt, DC electrical system.

A VOLTAGE REGULATOR regulates the charging voltage that the alternator produces, keeping it between 13.5 and 14.5 volts to protect the electrical components throughout the vehicle.

There is also a system to warn the driver if something is not right with the charging system.  This could be a dash mounted voltmeter, an ammeter, or more commonly, a warning lamp.  This lamp is variously labeled “Gen” Bat” and “Alt.”.  If this warning lamp lights up while the engine is running, it means that there is a problem in the charging system, usually an alternator that has stopped working.  The most common cause is a broken alternator drive belt.

Serpentine Belt: The alternator is driven by a belt that is powered by the rotation of the engine.  This belt goes around a pulley connected to the front of the engine’s crankshaft and is usually responsible for driving a number of other components including the water pump, power steering pump and air conditioning compressor.  On some engines, there is more than one belt and the task of driving these components is divided between them.  These belts are usually referred to as: Fan Belt, Alternator Belt, Drive Belt, Power Steering Belt, A/C Belt, etc.  More common on late model engines, one belt, called a Serpentine Belt will snake around the front of the engine and drive all the components by itself.

On engines with separate belts for each component, the belts will require periodic adjustments to maintain the proper belt tension.  On engines that use a serpentine belt, there is usually a spring loaded belt tensioner that maintains the tension of the belt, so no periodic adjustments are required. A serpentine belt is designed to last around 30,000 miles.  Check your owner’s manual to see how often yours should be replaced.

Alternator output is measured in both voltage and amperage.  To understand voltage and amperage, you must also know about resistance, which is measured in ohms.  An easy way to picture this is to compare the movement of electricity to that of running water.  Water flows through a pipe with a certain amount of pressure.  The size (diameter) of the pipe dictates how much resistance there will be to the flowing water.  The smaller the pipe, the more resistance.  You can increase the pressure to get more water to flow through, or you can increase the size of the pipe to allow more water to flow using less pressure.  Since too much pressure can burst the pipe, we should probably restrict the amount of pressure being used.  You get the idea, but how is this related to the flow of electricity?

Well, voltage is the same as water pressure.  Amperage is like the amount or volume of water flowing through, while resistance is the size of the wire transmitting the current.  Since too much voltage will damage the electrical components such as light bulbs and computer circuits, we must limit  the amount of voltage.  This is the job of the voltage regulator.  Too much water pressure and things could start breaking.  Too much voltage and things could start burning out.
Let’s get technical

Now, let’s go a little deeper and see how these charging system components actually work to produce the electrical power that a modern automobile requires.

The Alternator

• Alternator Stator – The alternator uses the principle of electromagnetism to produce current.  The way this works is simple.  If you take a strong magnet and pass it across a wire, that wire will generate a small voltage.  Take that same wire and loop it many times, than if you pass the same magnet across the bundle of loops, you create a more sizable voltage in that wire. There are two main components that make up an alternator.  They are the rotor and the stator.  The rotor is connected directly to the alternator pulley.  The drive belt spins the pulley, which in turn spins the rotor.  The stator is mounted to the body of the alternator and remains stationary.  There is just enough room in the center of the stator for the rotor to fit and be able to spin without making any contact. The stator contains 3 sets of wires that have many loops each and are evenly distributed to form a three phase system.  On some systems, the wires are connected to each other at one end and are connected to a rectifier assembly on the other end.  On other systems, the wires are connected to each other end to end, and at each of the three connection points, there is also a connection to the rectifier.  More on what a rectifier is later.

• Alternator Rotor – The rotor contains the powerful magnet that passes close to the many wire loops that make up the stator.  The magnets in the rotor are actually electromagnets, not a permanent magnets.  This is done so that we can control how much voltage the alternator produces by regulating the amount of current that creates the magnetic field in the rotor.  In this way, we can control the output of the alternator to suit our needs, and protect the circuits in the automobile from excessive voltage.

Now we know that every magnet has a north and a south pole and electro magnets are no exception.  Our rotor has two interlocking sections of electro magnets that are arranged so that there are fingers of alternating north and south poles, that are evenly distributed on the outside of the rotor. When we spin the rotor inside the stator and apply current to the rotor through a pair of brushes that make constant contact with two slip rings on the rotor shaft.  This causes the rotor to become magnetized.  The alternating north and south pole magnets spin past the three sets of wire loops in the stator and produce a constantly reversing voltage in the three wires.  In other words, we are producing alternating current in the stator.

Now, we have to convert this alternating current to direct current current.  This is done by using a series of 6 diodes that are mounted in a rectifier assembly.   A diode allows current to flow only in one direction.   If voltage tries to flow in the other direction, it is blocked.  The six diodes are arranged so that all the voltage coming from the alternator is aligned in one direction thereby converting AC current into DC current.

Typical Alternator Circuit -There are 2 diodes for each of the three sets of windings in the stator.  The two diodes are facing in opposite directions, one with its north pole facing the windings and the other with its south pole facing the windings.  This arrangement causes the AC current coming out of the windings to be converted to DC current before it leaves the alternator through the B terminal.  Connected to the B terminal of the alternator is a fairly heavy wire that runs straight to the battery.

Current to generate the magnetic field in the rotor comes from the ignition switch and passes through the voltage regulator.  Since the rotor is spinning, we need a way to connect this current from the regulator to the spinning rotor.  This is accomplished by wires connected to two spring loaded brushes that rub against two slip rings on the rotor’s shaft.  The voltage regulator monitors the voltage coming out of the alternator and, when it reaches a threshold of about 14.5 volts, the regulator reduces the current in the rotor to weaken the magnetic field.  When the voltage drops below this threshold, the current to the rotor is increased.

There is another circuit in the alternator to control the charging system warning lamp that is on the dash.  Part of that circuit is another set of diodes mounted inside the alternator called the diode trio.  The diode trio takes current coming from the three stator windings and passes a small amount through three diodes so that only the positive voltage comes through.  After the diodes, the wires are joined into one wire and sent out of the alternator at the L connection.  It then goes to one side of the dash warning lamp that is used to tell you when there is a problem with the charging system.  The other side of the lamp is connected to the run side of the ignition switch.  If both sides of the warning lamp have equal positive voltage, the lamp will not light.  Remove voltage from one side and the lamp comes on to let you know there is a problem.

This system is not very efficient.  There are many types of malfunctions of the charging system that it cannot detect, so just because the lamp is not lit does not mean everything is ok.  A volt meter is probably the best method of determining whether the charging system is working properly.
The Voltage Regulator
The voltage regulator can be mounted inside or outside of the alternator housing.  If the regulator is mounted outside (common on some Ford products) there will be a wiring harness connecting it to the alternator.

The voltage regulator controls the field current applied to the spinning rotor inside the alternator. When there is no current applied to the field, there is no voltage produced from the alternator. When voltage drops below 13.5 volts, the regulator will apply current to the field and the alternator will start charging. When the voltage exceeds 14.5 volts, the regulator will stop supplying voltage to the field and the alternator will stop charging. This is how voltage output from the alternator is regulated. Amperage or current is regulated by the state of charge of the battery. When the battery is weak, the electromotive force (voltage) is not strong enough to hold back the current from the alternator trying to recharge the battery. As the battery reaches a state of full charge, the electromotive force becomes strong enough to oppose the current flow from the alternator, the amperage output from the alternator will drop to close to zero, while the voltage will remain at 13.5 to 14.5. When more electrical power is used, the electromotive force will reduce and alternator amperage will increase. It is extremely important that when alternator efficiency is checked, both voltage and amperage outputs are checked. Each alternator has a rated amperage output depending on the electrical requirements of the vehicle.

Charging system gauge or warning lamp
The charging system gauge or warning lamp monitors the health of the charging system so that you have a warning of a problem before you get stuck.

When a charging problem is indicated, you can still drive a short distance to find help unlike an oil pressure or coolant temperature problem which can cause serious engine damage if you continue to drive. The worst that can happen with a charging system problem is that you get stuck in a bad location.

A charging system warning lamp is a poor indicator of problems in that there are many charging problems that it will not recognize. If it does light while you are driving, it usually means the charging system is not working at all. The most common cause of this is a broken alternator belt.

There are two types of gauges used to monitor charging systems on some vehicles: a voltmeter which measures system voltage and an ammeter which measures amperage. Most modern cars that have gauges use a voltmeter because it is a much better indicator of charging system health. A mechanic’s voltmeter is usually the first tool a technician uses when checking out a charging system

Typical Voltmeter – A modern automobile has a 12 volt electrical system. A fully charged battery will read about 12.5 volts when the engine is not running. When the engine is running, the charging system takes over so that the voltmeter will read 14 to 14.5 volts and should stay there unless there is a heavy load on the electrical system such as wipers, lights, heater and rear defogger all operating together while the engine is idling at which time the voltage may drop. If the voltage drops below 12.5, it means that the battery is providing some of the current. You may notice that your dash lights dim at this point. If this happens for an extended period, the battery will run down and may not have enough of a charge to start the car after shutting it off.  This should never happen with a healthy charging system because as soon as you step on the gas, the charging system will recharge the battery.  If the voltage is constantly below 14 volts, you should have the system checked. If the voltage ever goes above 15 volts, there is a problem with the voltage regulator. Have the system checked as soon as possible as this “overcharging” condition can cause damage to your electrical system.

Typical Ammeter – If you think of electricity as water, voltage is like water pressure, whereas amperage is like the volume of water.  If you increase pressure, then more water will flow through a given size pipe, but if you increase the size of the pipe, more water will flow at a lower pressure.  An ammeter will read from a negative amperage when the battery is providing most of the current thereby depleting itself, to a positive amperage if most of the current is coming from the charging system.  If the battery is fully charged and there is minimal electrical demand, then the ammeter should read close to zero, but should always be on the positive side of zero. It is normal for the ammeter to read a high positive amperage in order to recharge the battery after starting, but it should taper off in a few minutes.  If it continues to read more than 10 or 20 amps even though the lights, wipers and other electrical devices are turned off, you may have a weak battery and should have it checked.

What can go wrong?

There are a number of things that can go wrong with a charging system:

*Insufficient Charging Output
If one of the three stator windings failed, the alternator would still charge, but only at two thirds of its normal output.  Since an alternator is designed to handle all the power that is needed under heavy load conditions, you may never know that there is a problem with the unit.  It might only become apparent on a dark, cold rainy night when the lights, heater, windshield wipers and possible the seat heaters and rear defroster are all on at once that you may notice the lights start to dim as you slow down.  If two sets of windings failed, you will probably notice it a lot sooner

It is more common for one or more of the six diodes in the rectifier to fail.  If a diode burns out and opens one of the circuits, you would see the same problem as if one of the windings had failed.  The alternator will run at a reduced output.  However, if one of the diodes were to short out and allow current to pass in either direction, other problems will occur.  A shorted diode will allow AC current to pass through to the automobile’s electrical system which can cause problems with the computerized sensors and processors.  This condition can cause the car to act unpredictably and cause all kinds of problems.

*Too much voltage
A voltage regulator is designed to limit the voltage output of an alternator to 14.5 volts or less to protect the vehicle’s electrical system.  If the regulator malfunctions and allows uncontrolled voltage to be released, you will see bulbs and other electrical components begin to fail.  This is a dangerous and potentially costly problem.  Fortunately, this type of failure is very rare.  Most failures cause a reduction of voltage or amperage.

*Noise
Since the rotor is always spinning while the engine is running, there needs to be bearings to support the shaft and allow it to spin freely.  If one of those bearings were to fail, you will hear a grinding noise coming from the alternator.  A mechanic’s stethoscope can be used to confirm which of the spinning components driven by the serpentine belt is making the noise.
Repairing Charging System Problems

The most common repair is the replacement of the alternator with a new or rebuilt one.  A properly rebuilt alternator is as good as a new alternator and can cost hundreds less than purchasing a brand new one.

Labor time to replace an alternator is typically under an hour unless your alternator is in a hard to access location.  Most alternators are easily accessible and visible on the top of the engine.

Replacing an alternator is usually an easy task for a backyard mechanic and rebuilt alternators are readily available for most vehicles at the local auto parts store.  The most important task for the do-it-yourselfer is to be careful not to short anything out.  ALWAYS DISCONNECT THE BATTERY BEFORE REPLACING AN ALTERNATOR.

Alternators can be repaired by a knowledgeable technician, but in most cases, it is not economical to do this.  Also, since the rest of the alternator is not touched, a repair job is usually not guaranteed.

In some cases, if the problem is diagnosed as a bad voltage regulator, the regulator can be replaced without springing for a complete rebuild.  The problem with this is that there will be an extra labor charge for disassembling the alternator in order to get to the internal regulator.  That extra cost, along with the cost of the replacement regulator, will bring the total cost close to the cost of a complete (and guaranteed) rebuilt.

This is not the case when the regulator is not inside the alternator.  In those cases, the usual practice is to just replace the part that is bad.

This content is provided to you by All Makes Automotive Services.

All-Makes is the place to go for all your auto repair needs in Rio Rancho, NM.

Cooling System

What is a Cooling System?

A typical 4 cylinder vehicle cruising along the highway at around 50 miles per hour,  will produce 4000 controlled explosions per minute inside the engine as the spark plugs ignite the fuel in each cylinder to propel the vehicle down the road.  Obviously, these explosions produce an enormous amount of heat and, if not controlled, will destroy an engine in a matter of minutes.  Controlling these high temperatures is the job of the cooling system.

The modern cooling system has not changed much from the cooling systems in the model T back in the ’20s.  Oh sure, it has become infinitely more reliable and efficient at doing it’s job, but the basic cooling system still consists of liquid coolant being circulated through the engine, then out to the radiator to be cooled by the air stream coming through the front grill of the vehicle.

Today’s cooling system must maintain the engine at a constant temperature whether the outside air temperature is 110 degrees Fahrenheit  or 10 below zero.  If the engine temperature is too low, fuel economy will suffer and emissions will rise.  If the temperature is allowed to get too hot for too long, the engine will self destruct.
How Does a Cooling System Work?

Actually, there are two types of cooling systems found on motor vehicles:  Liquid cooled and Air cooled.  Air cooled engines are found on a few older cars, like the original Volkswagen Beetle, the Chevrolet Corvair and a few others.  Many modern motorcycles still use air cooling, but for the most part, automobiles and trucks use liquid cooled systems and that is what this article will concentrate on.

The cooling system is made up of the passages inside the engine block and heads, a  water pump to circulate the coolant, a thermostat to control the temperature of the coolant, a radiator to cool the coolant, a radiator cap to control the pressure in the system, and some plumbing consisting of interconnecting hoses to transfer the coolant from the engine to radiator and also to the car’s heater system where hot coolant is used to warm up the vehicle’s interior on a cold day.

A cooling system works by sending a liquid coolant through passages in the engine block and heads.  As the coolant flows through these passages, it picks up heat from the engine.  The heated fluid then makes its way through a rubber hose to the radiator in the front of the car.  As it flows through the thin tubes in the radiator, the hot liquid is cooled by the air stream entering the engine compartment from the grill in front of the car.  Once the fluid is cooled, it returns to the engine to absorb more heat.  The water pump has the job of keeping the fluid moving through this system of plumbing and hidden passages.

A thermostat is placed between the engine and the radiator to make sure that the coolant stays above a certain preset temperature.  If the coolant temperature falls below this temperature, the thermostat blocks the coolant flow to the radiator, forcing the fluid instead through a bypass directly back to the engine.  The coolant will continue to circulate like this until it reaches the design temperature, at which point, the thermostat will open a valve and allow the coolant back through the radiator.

In order to prevent the coolant from boiling, the cooling system is designed to be pressurized.  Under pressure, the boiling point of the coolant is raised considerably.  However, too much pressure will cause hoses and other parts to burst, so a system is needed to relieve pressure if it exceeds a certain point.  The job of maintaining the pressure in the cooling system belongs to the radiator cap.  The cap is designed to release pressure if it reaches the specified upper limit that the system was designed to handle.  Prior to the ’70s, the cap would release this extra pressure to the pavement.  Since then, a system was added to capture any released fluid and store it temporarily in a reserve tank.  This fluid would then return to the cooling system after the engine cooled down.  This is what is called a closed cooling system.

Circulation
The coolant follows a path that takes it from the water pump, through passages inside the engine block where it collects the heat produced by the cylinders.  It then flows up to the cylinder head (or heads in a V type engine) where it collects more heat from the combustion chambers.  It then flows out past the thermostat (if the thermostat is opened to allow the fluid to pass), through the upper radiator hose and into the radiator.  The coolant flows through the thin flattened tubes that make up the core of the radiator and is cooled by the air flow through the radiator.  From there, it flows out of the radiator, through the lower radiator hose and back to the water pump.  By this time, the coolant is cooled off and ready to collect more heat from the engine.

The capacity of the system is engineered for the type and size of the engine and the work load that it is expected to undergo.  Obviously, the cooling system for a larger, more powerful V8 engine in a heavy vehicle will need considerably more capacity then a compact car with a small 4 cylinder engine.  On a large vehicle, the radiator is larger with many more tubes for the coolant to flow through.  The radiator is also wider and taller to capture more air flow entering the vehicle from the grill in front.

Antifreeze
The coolant that courses through the engine and associated plumbing must be able to withstand temperatures well below zero without freezing.  It must also be able to handle engine temperatures in excess of 250 degrees without boiling.  A tall order for any fluid, but that is not all.  The fluid must also contain rust inhibiters and a lubricant.

The coolant in today’s vehicles is a mixture of ethylene glycol (antifreeze) and water.  The recommended ratio is fifty-fifty.  In other words, one part antifreeze and one part water.  This is the minimum recommended for use in automobile engines.  Less antifreeze and the boiling point would be too low.  In certain climates where the temperatures can go well below zero, it is permissible to have as much as 75% antifreeze and 25% water, but no more than that.  Pure antifreeze will not work properly and can cause a boil over.

Antifreeze is poisonous and should be kept away from people and animals, especially dogs and cats, who are attracted by the sweet taste.  Ethylene Glycol, if ingested, will form calcium oxalate crystals in the kidneys which can cause acute renal failure and death.

The Components of a Cooling System

* The Radiator
* Radiator Cooling Fans
* Pressure Cap & Reserve Tank
* Water Pump
* Thermostat
* Bypass System
* Freeze Plugs
* Head Gaskets & Intake Manifold Gaskets
* Heater Core
* Hoses

The Radiator
The radiator core is usually made of flattened aluminum tubes with aluminum strips that zigzag between the tubes.  These fins transfer the heat in the tubes into the air stream to be carried away from the vehicle.  On each end of the radiator core is a tank, usually made of plastic that covers the ends of the radiator.

On most modern radiators, the tubes run horizontally with the plastic tank on either side.  On other cars, the tubes run vertically with the tank on the top and bottom.  On older vehicles, the core was made of copper and the tanks were brass.  The new aluminum-plastic system is much more efficient, not to mention cheaper to produce.  On radiators with plastic end caps, there are gaskets between the aluminum core and the plastic tanks to seal the system and keep the fluid from leaking out.  On older copper and brass radiators, the tanks were brazed (a form of welding) in order to seal the radiator.

The tanks, whether plastic or brass, each have a large hose connection, one mounted towards the top of the radiator  to let the coolant in, the other mounted at the bottom of the radiator on the other tank to let the coolant back out.  On the top of the radiator is an additional opening that is capped off by the radiator cap.

Another component in the radiator for vehicles with an automatic transmission is a separate tank mounted inside one of the tanks.  Fittings connect this inner tank through steel tubes to the automatic transmission.  Transmission fluid is piped through this tank inside a tank to be cooled by the coolant flowing past it before returning the the transmission.

Radiator Fans
Mounted on the back of the radiator on the side closest to the engine is one or two electric fans inside a housing that is designed to protect fingers and to direct the air flow.  These fans are there to keep the air flow going through the radiator while the vehicle is going slow or is stopped with the engine running.  If these fans stopped working, every time you came to a stop, the engine temperature would begin rising.  On older systems, the fan was connected to the front of the water pump and would spin whenever the engine was running because it was driven by a fan belt instead of an electric motor.  In these cases, if a driver would notice the engine begin to run hot in stop and go driving, the driver might put the car in neutral and rev the engine to turn the fan faster which helped cool the engine.  Racing the engine on a car with a malfunctioning electric fan would only make things worse because you are producing more heat in the radiator with no fan to cool it off.

The electric fans are controlled by the vehicle’s computer.  A temperature sensor monitors engine temperature and sends this information to the computer.  The computer determines if the fan should be turned on and actuates the fan relay if additional air flow through the radiator is necessary.

If the car has air conditioning, there is an additional radiator mounted in front of the normal radiator.  This “radiator” is called the air conditioner condenser, which also needs to be cooled by the air flow entering the engine compartment.  You can find out more about the air conditioning condenser by going to our article on Automotive Air Conditioning.  As long as the air conditioning is turned on, the system will keep the fan running, even if the engine is not running hot.  This is because if there is no air flow through the air conditioning condenser, the air conditioner will not be able to cool the air entering the interior.

Pressure cap and reserve tank
As coolant gets hot, it expands.  Since the cooling system is sealed, this expansion causes an increase in pressure in the cooling system, which is normal and part of the design.  When coolant is under pressure, the temperature where the liquid begins to boil is considerably higher.  This pressure, coupled with the higher boiling point of ethylene glycol, allows the coolant to safely reach temperatures in excess of 250 degrees.

The radiator pressure cap is a simple device that will maintain pressure in the cooling system up to a certain point.  If the pressure builds up higher than the set pressure point, there is a spring loaded valve, calibrated to the correct Pounds per Square Inch (psi), to release the pressure.

When the cooling system pressure reaches the point where the cap needs to release this excess pressure, a small amount of coolant is bled off.  It could happen during stop and go traffic on an extremely hot day, or if the cooling system is malfunctioning.  If it does release pressure under these conditions, there is a system in place to capture the released coolant and store it in a plastic tank that is usually not pressurized.  Since there is now less coolant in the system, as the engine cools down a partial vacuum is formed.  The radiator cap on these closed systems has a secondary valve to allow the vacuum in the cooling system to draw the coolant back into the radiator from the reserve tank (like pulling the plunger back on a hypodermic needle)  There are usually markings on the side of the plastic tank marked Full-Cold, and Full Hot.  When the engine is at normal operating temperature, the coolant in the translucent reserve tank should be up to the Full-Hot line.  After the engine has been sitting for several hours and is cold to the touch, the coolant should be at the Full-Cold line.

Water Pump
A water pump is a simple device that will keep the coolant moving as long as the engine is running.  It is usually mounted on the front of the engine and turns whenever the engine is running.  The water pump is driven by the engine through one of the following:
* A fan belt that will also be responsible for driving an additional component like an alternator or power steering pump
* A serpentine belt, which also drives the alternator, power steering pump and AC compressor among  other things.
* The timing belt that is also responsible for driving one or more camshafts.

The water pump is made up of a housing, usually made of cast iron or cast aluminum and an impeller mounted on a spinning shaft with a pulley attached to the shaft on the outside of the pump body.  A seal keeps fluid from leaking out of the pump housing past the spinning shaft.  The impeller uses centrifugal force to draw the coolant in from the lower radiator hose and send it under pressure into the engine block.  There is a gasket to seal the water pump to the engine block and prevent the flowing coolant from leaking out where the pump is attached to the block.

Thermostat
The thermostat is simply a valve that measures the temperature of the coolant and, if it is hot enough, opens to allow the coolant to flow through the radiator.  If the coolant is not hot enough, the flow to the radiator is blocked and fluid is directed to a bypass system that allows the coolant to return directly back to the engine.  The bypass system allows the coolant to keep moving through the engine to balance the temperature and avoid hot spots.  Because flow to the radiator is blocked, the engine will reach operating temperature sooner and, on a cold day, will allow the heater to begin supplying hot air to the interior more quickly.

Since the 1970s, thermostats have been calibrated to keep the temperature of the coolant above 192 to 195 degrees.  Prior to that, 180 degree thermostats were the norm.  It was found that if the engine is allowed to run at these hotter temperatures, emissions are reduced, moisture condensation inside the engine is quickly burned off extending engine life, and combustion is more complete which improves fuel economy.

The heart of a thermostat is a sealed copper cup that contains wax and a metal pellet.  As the thermostat heats up, the hot wax expands, pushing a piston against spring pressure to open the valve and allow coolant to circulate.

The thermostat is usually located in the front, top part of the engine in a water outlet housing that also serves as the connection point for the upper radiator hose.  The thermostat housing attaches to the engine, usually with two bolts and a gasket to seal it against leaks.  The gasket is usually made of a heavy paper or a rubber O ring is used.  In some applications, there is no gasket or rubber seal.  Instead, a thin bead of special silicone sealer is squeezed from a tube to form a seal.

There is a mistaken belief by some people that if they remove the thermostat, they will be able to solve hard to find overheating problems.  This couldn’t be further from the truth.  Removing the thermostat will allow uncontrolled circulation of the coolant throughout the system.  It is possible for the coolant to move so fast, that it will not be properly cooled as it races through the radiator, so the engine can run even hotter than before under certain conditions.  Other times, the engine will never reach its operating temperature.  On computer controlled vehicles, the computer monitors engine temperatures and regulates fuel usage based on that temperature.  If the engine never reaches operating temperatures, fuel economy and performance will suffer considerably.

Bypass System
This is a passage that allows the coolant to bypass the radiator and return directly back to the engine.  Some engines use a rubber hose, or a fixed steel tube.  In other engines, there is a cast in passage built into the water pump or front housing.  In any case, when the thermostat is closed, coolant is directed to this bypass and channeled back to the water pump, which sends the coolant back into the engine without being cooled by the radiator.

Freeze Plugs
When an engine block is manufactured, a special sand is molded to the shape of the coolant passages in the engine block.  This sand sculpture is positioned inside a mold and molten iron or aluminum is poured to form the engine block.  When the casting is cooled, the sand is loosened and removed through holes in the engine block casting leaving the passages that the coolant flows through.    Obviously, if we don’t plug up these holes, the coolant will pour right out.

Plugging these holes is the job of the freeze-out plug.  These plugs are steel discs or cups that are press fit in the holes in the side of the engine block and normally last the life of the engine with no problems.  But there is a reason they are called freeze-out plugs.  In the early days, many people used plain water in their engines, usually after replacing a burst hose or other cooling system repair.  “It is summer and I will replace the water with antifreeze when the weather starts turning”.

Needless to say, people are forgetful and many a motor suffered the fate of the water freezing inside the block.  Often, when this happened the pressure of the water freezing and expanding forced the freeze-out plugs to pop out, relieving the pressure and saving the engine block from cracking. (although, just as often the engine cracked anyway).  Another reason for these plugs to fail was the fact that they were made of steel and would easily rust through if the vehicle owner was careless about maintaining the cooling system.  Antifreeze has rust inhibitors in the formula to prevent this from happening, but those chemicals would lose their effect after 3 years, which is why antifreeze needs to be changed periodically.  The fact that some people left plain water in their engines greatly accelerated the rusting of these freeze plugs.

When a freeze plug becomes so rusty that it perforates, you have a coolant leak that must be repaired by replacing the rusted out freeze plug with a new one.  This job ranges from fairly easy to extremely difficult depending on the location of the affected freeze plug.  Freeze plugs are located on the sides of the engine, usually 3 or 4 per side.  There are also freeze plugs on the back of the engine on some models and also on the heads.

As long as you are good about maintaining the cooling system, you need never worry about these plugs failing on modern vehicles

Head Gaskets and Intake Manifold Gaskets
All internal combustion engines have an engine block and one or two cylinder heads.  The mating surfaces where the block and head meet are machined flat for a close, precision fit, but no amount of careful machining will allow them to be completely water tight or be able to hold back combustion gases from escaping past the mating surfaces.

In order to seal the block to the heads, we use a head gasket.  The head gasket has several things it needs to seal against.  The main thing is the combustion pressure on each cylinder.  Oil and coolant must easily flow between block and head and it is the job of the head gasket to keep these fluids from leaking out or into the combustion chamber, or each other for that matter.

A typical head gasket is usually made of soft sheet metal that is stamped with ridges that surround all leak points.  When the head is placed on the block, the head gasket is sandwiched between them.  Many bolts, called head bolts are screwed in and tightened down causing the head gasket to crush and form a tight seal between the block and head.

Head gaskets usually fail if the engine overheats for a sustained period of time causing the cylinder head to warp and release pressure on the head gasket.  This is most common on engines with cast aluminum heads, which are now on just about all modern engines.

Once coolant or combustion gases leak past the head gasket, the gasket material is usually damaged to a point where it will no longer hold the seal.  This causes leaks in several possible areas.

For example:
* Combustion gases could leak into the coolant passages causing excessive pressure in the cooling system.
* Coolant could leak into the combustion chamber causing coolant to escape through the exhaust system, often causing a white cloud of smoke at the tailpipe.
* Other problems such as oil mixing with the coolant or being burned out the exhaust are also possible.

Some engines are more susceptible to head gasket failure than others.  I have seen blown head gaskets on engines that just started to overheat and were running hot for less than 5 minutes.  The best advice I can give is, if the engine shows signs of overheating, find a place to pull over and shut the engine off as quickly as possible.

Head gaskets themselves are relatively cheap, but it is the labor that’s the killer.  A typical head gasket replacement is a several hour job where the top part of the engine must be completely disassembled.  These jobs can easily reach $1,000 or more.

On V type engines, there are two heads, meaning two head gaskets.  While the labor won’t double if both head gaskets need to be replaced, it will probably add a good 30% more labor to replace both.  If only one head gasket has failed, it is usually not necessary to replace both, but it could be added insurance to get them both done at once.

A head gasket replacement begins with the diagnosis that the head gasket has failed.  There is no way for a technician to know for certain whether there is additional damage to the cylinder head or other components without first disassembling the engine.  All he or she knows is that fluid and/or combustion is not being contained.

One way to tell if a head gasket has failed is through a combustion leak test on the radiator.  This is a chemical test that determines if there are combustion gases in the engine coolant.  Another way is to remove the spark plugs and crank the engine while watching for water spray from one or more spark plug holes.  Once the technician has determined that a head gasket must be replaced, an estimate is given for parts and labor.  The technician will then explain that there may be additional charges after the engine is opened if more damage is found.

Heater Core
The hot coolant is also used to provide heat to the interior of the vehicle when needed.   This is a simple and straight forward system that includes a heater core, which looks like a small version of a radiator, connected to the cooling system with a pair of rubber hoses.  One hose brings hot coolant from the water pump to the heater core and the other hose returns the coolant to the top of the engine.  There is usually a heater control valve in one of the hoses to block the flow of coolant into the heater core when maximum air conditioning is called for.

A fan, called a blower, draws air through the heater core and directs it through the heater ducts to the interior of the car.  Temperature of the heat is regulated by a blend door that mixes cool outside air, or sometimes air conditioned air with the heated air coming through the heater core.  This blend door allows you to control the temperature of the air coming into the interior.  Other doors allow you to direct the warm air through the ducts on the floor, the defroster ducts at the base of the windshield, and the air conditioning ducts located in the instrument panel.

Hoses
There are several rubber hoses that make up the plumbing to connect the components of the cooling system.  The main hoses are called the upper and lower radiator hoses.  These two hoses are approximately 2 inches in diameter and direct coolant between the engine and the radiator.  Two additional hoses, called heater hoses, supply hot coolant from the engine to the heater core.  These hoses are approximately 1 inch in diameter.  One of these hoses may have a heater control valve mounted in-line to block the hot coolant from entering the heater core when the air conditioner is set to max-cool.  A fifth hose, called the bypass hose, is used to circulate the coolant through the engine, bypassing the radiator, when the thermostat is closed.  Some engines do not use a rubber hose.  Instead, they might use a metal tube or have a built-in passage in the front housing.

These hoses are designed to withstand the pressure inside the cooling system.  Because of this, they are subject to wear and tear and eventually may require replacing as part of routine maintenance.  If the rubber is beginning to look dry and cracked, or becomes soft and spongy, or you notice some ballooning at the ends, it is time to replace them.  The main radiator hoses are usually molded to a shape that is designed to rout the hose around obstacles without kinking.  When purchasing replacements, make sure that they are designed to fit the vehicle.

There is a small rubber hose that runs from the radiator neck to the reserve bottle.  This allows coolant that is released by the pressure cap to be sent to the reserve tank.  This rubber hose is about a quarter inch in diameter and is normally not part of the pressurized system.  Once the engine is cool, the coolant is drawn back to the radiator by the same hose.

Cooling System Maintenance and Repair
An engine that is overheating will quickly self destruct, so proper maintenance of the cooling system is very important to the life of the engine and the trouble free operation of the cooling system in general.

The most important maintenance item is to flush and refill the coolant periodically.  The reason for this important service is that anti-freeze has a number of additives that are designed to prevent corrosion in the cooling system.  This corrosion tends to accelerate when several different types of metal interact with each other.  The corrosion causes scale that eventually builds up and begins to clog the thin flat tubes in the radiator and heater core, causing the engine to eventually overheat.  The anti-corrosion chemicals in the antifreeze prevents this, but they have a limited life span.

Newer antifreeze formulations will last for 5 years or 150,000 miles before requiring replacement.  These antifreezes are usually red in color and are referred to as “Extended Life” or “Long Life” antifreeze.  GM has been using this type of coolant in all their vehicles since 1996.  The GM product is called “Dex-Cool”.

Most antifreeze used in vehicles however, is green in color and should be replaced every two years or 30,000 miles, which ever comes first.  You can convert to the new long life coolant, but only if you completely flush out all of the old antifreeze.  If any green coolant is allowed to mix with the red coolant, you must revert to the shorter replacement cycle.

Sometimes, you may need a reverse-flush of the cooling system.  This requires special equipment and the removal of the thermostat in order to do the job properly.  This type of flush is especially important if the old coolant looks brown or has scale or debris floating around in it.

If you remove the thermostat for a reverse flush, always replace it with a new thermostat of the proper temperature.  It is cheap insurance.

The National Automotive Radiator Service Association (NARSA) recommends that motorists have a seven-point preventative cooling system maintenance check at least once every two years. The seven-point program is designed to identify any areas that need attention.

It consists of:
* a visual inspection of all cooling system components, including belts and hoses
* a radiator pressure cap test to check for the recommended system pressure level
* a thermostat check for proper opening and closing
* a pressure test to identify any external leaks to the cooling system parts; including the radiator, water pump, engine coolant passages, radiator and heater hoses and heater core
* an internal leak test to check for combustion gas leakage into the cooling system
* an engine fan test for proper operation
* a system power flush and refill with car manufacturer’s recommended concentration of coolant

Let’s take these items one at a time.

Visual Inspection
What you are looking for is the condition of the belts and hoses.  The radiator hoses and heater hoses are easily inspected just by opening the hood and looking.  You want to be sure that the hoses have no cracking or splitting and that there is no bulging or swelling at the ends.  If there is any sign of problems, the hose should be replaced with the correct part number for the year, make and model of the vehicle.  Never use a universal hose unless it is an emergency and a proper molded hose is not available.

Heater hoses are usually straight runs and are not molded, so a universal hose is fine to use and often is all that is available.  Make sure that you use the proper inside diameter for the hose being replaced.  For either the radiator hoses or the heater hoses, make sure that you route the replacement hose in the same way that the original hose was running.  Position the hose away from any obstruction that can possibly damage it and always use new hose clamps.  After you refill the cooling system with coolant, do a pressure test to make sure that there are no leaks.

On most older vehicles, the water pump is driven by a V belt or serpentine belt on the front of the engine that is also responsible for driving the alternator, power steering pump and air conditioner compressor.  These types of belts are easy to inspect and replace if they are worn.  You are looking for dry cracking on the inside surface of the belt.

On later vehicles, the water pump is often driven by the timing belt.  This belt usually has a specific life expectancy at which time it must be replaced to insure that it does not fail.  Since the timing belt is inside the engine and will require partial engine disassembly to inspect, it is very important to replace it at the correct interval.  Since the labor to replace this belt can be significant, it is a good idea to replace the water pump at the same time that the belt is replaced.  This is because 90 percent of the labor to replace a water pump has already been done to replace the timing belt.  It is simply good insurance to replace the pump while everything is apart.

Radiator pressure cap test
A radiator pressure cap is designed to maintain pressure in the cooling system at a certain maximum pressure.  If the cooling system exceeds that pressure, a valve in the cap opens to bleed the excessive pressure into the reserve tank.  Once the engine has cooled off, a negative pressure begins to develop in the cooling system.  When this happens, a second valve in the cap allows the coolant to be siphoned back into the radiator from the reserve tank.  If the cap should fail, the engine can easily overheat.  A pressure test of the radiator cap is a quick way to tell if the cap is doing its job.  It should be able to hold its rated pressure for two minutes.  Since radiator caps are quite inexpensive, I would recommend replacing it every 3 years or 36,000 miles, just for added insurance.  Make absolutely sure that you replace it with one that is designed for your vehicle.

Thermostat check for proper opening and closing
This step is only necessary if you are having problems with the cooling system.
A thermostat is designed to open at a certain coolant temperature.  To test a thermostat while it is still in the engine, start the engine and let it come to normal operating temperature (do not let it overheat).  If it takes an unusually long time for the engine to warm up or for the heater to begin delivering hot air, the thermostat may be stuck in the open position.  If the engine does warm up, shut it off and look for the two radiator hoses.  These are the two large hoses that go from the engine to the radiator.  Feel them carefully (they could be very hot).  If one hose is hot and the other is cold, the thermostat may be stuck closed.

If you are having problems and suspect the thermostat, remove it and place it in a pot of water.  Bring the water to a boil and watch the thermostat.  You should see it open when the water reaches a boil.  Most thermostats open at about 195 degrees Fahrenheit.  An oven thermometer in the water should confirm that the thermostat is working properly.

Pressure test to identify any external leaks
Pressure testing the cooling system is a simple process to determine where a leak is located.  This test is only performed after the cooling system has cooled sufficiently to allow you to safely remove the pressure cap.  Once you are sure that the cooling system is full of coolant, a cooling system pressure tester is attached in place of the radiator cap.  The tester is than pumped to build up pressure in the system.  There is a gauge on the tester indicating how much pressure is being pumped.  You should pump it to the pressure indicated on the pressure cap or to manufacturer’s specs.

Once pressure is applied, you can begin to look for leaks.  Also watch the gauge on the tester to see if it loses pressure.  If the pressure drops more than a couple of pounds in two minutes, there is likely a leak somewhere that may be hidden.  It is not always easy to see where a leak is originating from.  It is best to have the vehicle up on a lift so you can look over everything with a shop light or flashlight.  If the heater core in leaking, it may not be visible since the core is enclosed and not visible without major disassembly, but one sure sign is the unmistakable odor of antifreeze inside the car.  You may also notice the windshield steaming up with an oily residue.

Internal leak test
If you are losing coolant, but there are no signs of leaks, you could have a blown head gasket.  The best way to test for this problem is with a combustion leak test on the radiator.  This is accomplished using a block tester.  This is a kit that performs a chemical test on the vapors in the radiator.  Blue tester fluid is added to the plastic container on the tester.  If the fluid turns yellow during the test, then exhaust gasses are present in the radiator.

The most common causes for exhaust gasses to be present in the radiator is a blown head gasket.  Replacing a bad head gasket requires a major disassembly of the engine and can be quite expensive.  Other causes include a cracked head or a cracked block, both are even more undesirable than having to replace a head gasket.

When a head gasket goes bad
The process of replacing a head gasket begins with completely draining the coolant from the engine.  The top part of the engine is then disassembled along with much of the front of the engine in order to gain access to the cylinder heads.  The head or heads are then removed and a thorough inspection for additional damage is done.

Before the engine can be reassembled, the mating surfaces of the head and block are first cleaned to make sure that nothing will interfere with the sealing properties of the gasket.  The surface of the cylinder head is also checked for flatness and, in some cases, the block is checked as well.  The head gasket is then positioned on the block and aligned using locator pegs that are built into the block.  The head is then placed on top of the gasket and a number of bolts, called head-bolts are coated with oil and loosely threaded into the assembly.  The bolts are then tightened in a specific order to a specified initial torque using a special wrench called a torque wrench.  This is to insure that the head gasket is crushed evenly in order to insure a tight seal.  This process is then repeated to a second, tighter torque setting, then finally a third torque setting.  At this point, the rest of the engine is reassembled and the cooling system is filled with a mixture of antifreeze and water.  Once the engine is filled, the technician will pressure test the cooling system to make sure there are no leaks.

In many engines, coolant also passes between the heads and the intake manifold.  There are also gaskets for the intake manifold to keep the coolant from leaking out at that point.  Replacing an intake manifold gasket is a much easier job than a head gasket, but can still take a couple of hours or more for that job.

Engine Fan Test
The radiator cooling fan is an important part of the cooling system operation.  While a fan is not really needed while a vehicle is traveling down the highway, it is extremely important when driving slowly or stopped with the engine running.  In the past, the fan was attached to the engine and was driven by the fan belt.  The speed of the fan was directly proportional to the speed of the engine.  This type of system sometimes caused excessive noise as the car accelerated through the gears.  As the engine sped up, a rushing fan noise could be heard.  To quiet things down and place less of a drag in the engine, a viscous fan drive was developed in order to disengage the fan when it was not needed.

When computer controls came into being, these engine driven fans gave way to electric fans that were mounted directly on the radiator.  A temperature sensor determined when the engine was beginning to run too hot and turned on the fan to draw air through the radiator to cool the engine.  On many cars, there were two fans mounted side by side to make sure that the radiator had a uniform air flow for the width of the unit.

When the car was in motion, the speed of the air entering the grill was sufficient to keep the coolant at the proper temperature, so the fans were shut off.  When the vehicle came to a stop, there was no natural air flow, so the fan would come on as soon as the engine reached a certain temperature.

If the air conditioner was turned on, a different circuit would come into play.  The reason for this is the air conditioning system always requires a good air flow through the condenser mounted in front of the radiator.  If the air flow stopped, the air conditioned air coming through the dash outlets would immediately start warming up.  For this reason, when the air conditioner is turned on, the fan circuit would power the fans regardless of engine temperature.

If you notice that the engine temperature begins rising soon after the vehicle comes to a stop, the first thing to check is fan operation.  If the fan is not turning when the engine is hot, a simple test is to turn the AC on.  If the fan begins to work, suspect the temperature sensor in the fan circuit (you will need a wiring diagram for your vehicle to find it).  In order to test the fan motor itself, unplug the two wire connector to the fan and connect a 12 volt source to one terminal and ground the other. (it doesn’t matter which is which for this test)  If the fan motor begins to turn, the motor is good.  If it doesn’t turn, the motor is bad and must be replaced.

In order to test the system further, you will need a repair manual for the year, make and model vehicle and follow the troubleshooting charts and diagnostic procedures for your vehicle.  On most systems, there will be a fan relay or fan control module that can be a trouble spot.  There are a number of different control systems, each requiring a different test procedure.  Without the proper repair information, you can easily do more harm than good.

Cooling system power flush and refill
While you can replace old coolant by draining it out and replacing it with fresh coolant, the best way to properly maintain your cooling system is to have the system power flushed.  Power flushing will remove all the old coolant and pull out any sediment and scale along with it.

Power flushing requires a special machine that All Makes Automotive Services has for that purpose.  The procedure requires that the thermostat is removed, the lower radiator hose is disconnected, and the flush machine is connected in line.  The lower hose is connected to the machine and the other hose from the machine is connected to the radiator where the lower hose was disconnected from.

Water, and sometimes, a cleaning agent is pumped through the cooling system in a reverse path from the normal coolant flow.  This allows any scale to be loosened and flow out.  Once clear water is coming out of the system, the hose is reconnected and a new thermostat is installed.  Then the cooling system is refilled with the appropriate amount of antifreeze to bring the coolant to the proper mixture of antifreeze and water.  For most vehicles and most climates, the mixture is 50 percent antifreeze and 50 percent water.  In colder climates, more antifreeze is used, but must never exceed 75 percent antifreeze.  Check your owner’s manual for the proper procedures and recommendations for your vehicle.

This content is provided to you by All Makes Automotive Services.

All-Makes is the place to go for all your auto repair needs in Rio Rancho, NM.

Engines

Internal combustion gasoline engines run on a mixture of gasoline and air.  The ideal mixture is 14.7 parts of  air to one part of gasoline (by weight.)  Since gas weighs much more than air, we are talking about a whole lot of air and a tiny bit of gas.   One part of gas that is completely vaporized into 14.7 parts of air can produce tremendous power when ignited inside an engine.

Let’s see how the modern engine uses that energy to make the wheels turn.

Air enters the engine through the air cleaner and proceeds to the throttle plate. You control the amount of air that passes through the throttle plate and into the engine with the gas pedal.  It is then distributed through a series of passages called the intake manifold, to each cylinder.  At some point after the air cleaner, depending on the engine, fuel is added to the air-stream by either a fuel injection system or, in older vehicles, by the carburetor.

Once the fuel is vaporized into the air stream, the mixture is drawn into each cylinder as that cylinder begins its intake stroke.  When the piston reaches the bottom of  the cylinder, the intake valve closes and the piston begins moving up in the cylinder compressing the charge.  When  the piston reaches the top, the spark plug ignites the fuel-air mixture causing a powerful expansion of the gas, which pushes the piston back down with great force against the crankshaft, just like a bicycle rider pushing against the pedals to make the bike go.

Let’s take a closer look at this process.

Engine Types
The majority of engines in motor vehicles today are four-stroke, spark-ignition internal combustion engines.  The exceptions like the diesel and rotary engines will not be covered in this article.

Typical Cylinder Arrangements: There are several engine types which are identified by the number of cylinders and the way the cylinders are laid out.  Motor vehicles will have from 3 to 12 cylinders which are arranged in the engine block in several configurations. In-line engines have their cylinders arranged in a row.   3, 4, 5 and 6 cylinder engines commonly use this arrangement. The “V” arrangement uses two banks of cylinders side-by-side and is commonly used in V-6, V-8, V-10 and V-12  configurations. Flat engines use two opposing banks of cylinders and are less common than the other two designs.  They are used in engines from Subaru and Porsche in 4 and 6 cylinder arrangements as well as in the old VW beetles with 4 cylinders.  Flat engines are also used in some Ferraris with 12 cylinders. Most engine blocks are made of cast iron or cast aluminum.

Piston and Connecting Rod: Each cylinder contains a piston that travels up and down inside the cylinder bore.  All the pistons in the engine are connected through individual connecting rods to a common crankshaft.

Crankshaft: The crankshaft is located below the cylinders on an in-line engine, at the base of the V on a V-type engine and between the cylinder banks on a flat engine. As the pistons move up and down, they turn the crankshaft just like your legs pump up and down to turn the crank that is connected to the pedals of a bicycle.
Typical Cylinder Head: A cylinder head is bolted to the top of each bank of cylinders to seal the individual cylinders and contain the combustion process that takes place inside the cylinder.  Most cylinder heads are made of cast aluminum or cast iron.  The cylinder head contains at least one intake valve and one exhaust valve for each cylinder. This allows the air-fuel mixture to enter the cylinder and the burned exhaust gas to exit the cylinder.  Engines have at least two valves per cylinder, one intake valve and one exhaust valve. Many newer engines are using multiple intake and exhaust valves per cylinder for increased engine power and efficiency.   These engines are sometimes named for the number of valves that they have such as “24 Valve V6″ which indicates a V-6 engine with four valves per cylinder.  Modern engine designs can use anywhere from 2 to 5 valves per cylinder.
Camshaft: The valves are opened and closed by means of a camshaft. A camshaft is a rotating shaft that has individual lobes for each valve.  The lobe is a “bump” on one side of the shaft that pushes against a valve lifter moving it up and down. When the lobe pushes against the lifter, the lifter in turn pushes the valve open.  When the lobe rotates away from the lifter, the valve is closed by a spring that is attached to the valve.   A common configuration is to have one camshaft located in the engine block with the lifters connecting to the valves through a series of linkages.  The camshaft must be synchronized with the crankshaft so that the camshaft makes one revolution for every two revolutions of the crankshaft.  In most engines, this is done by a “Timing Chain” (similar to a bicycle chain) that connects the camshaft with the crankshaft. Newer engines have the camshaft located in the cylinder head directly over the valves.  This design is more efficient but it is more costly to manufacture and requires multiple camshafts on Flat and V-type engines.  It also requires much longer timing chains or timing belts which are prone to wear.  Some engines have two camshafts on each head, one for the intake valves and one for the exhaust valves.  These engines are called Double Overhead Camshaft (D.O.H.C.) Engines while the other type is called Single Overhead Camshaft (S.O.H.C.) Engines.  Engines with the camshaft in the block are called Overhead Valve (O.H.V) Engines. Now when you see “DOHC 24 Valve V6″, you’ll know what it means.

How an Engine Works

Since the same process occurs in each cylinder, we will take a look at one cylinder to see how the four stroke process works.

The four strokes are Intake, Compression, Power and Exhaust. The piston travels down on the Intake stroke, up on the Compression stroke, down on the Power stroke and up on the Exhaust stroke. Running Engine

* Intake
As the piston starts down on the Intake stroke, the intake valve opens and the fuel-air mixture is drawn into the cylinder (similar to drawing back the plunger on a hypodermic needle to allow fluid to be drawn into the chamber.)
When the piston reaches the bottom of the intake stroke, the intake valve closes, trapping the air-fuel mixture in the cylinder.
* Compression
The piston moves up and compresses the trapped air fuel mixture that was brought in by the intake stroke. The amount that the mixture is compressed is determined by the compression ratio of the engine.  The compression ratio on the average engine is in the range of 8:1  to 10:1. This means that when the piston reaches the top of the cylinder, the air-fuel mixture is squeezed to about one tenth of its original volume.
* Power
The spark plug fires, igniting the compressed air-fuel mixture which produces a powerful expansion of the vapor.  The combustion process pushes the piston down the cylinder with great force turning the crankshaft to provide the power to propel the vehicle. Each piston fires at a different time, determined by the engine firing order. By the time the crankshaft completes two revolutions, each cylinder in the engine will have gone through one power stroke.
* Exhaust
With the piston at the bottom of the cylinder, the exhaust valve opens to allow the burned exhaust gas to be expelled to the exhaust system.   Since the cylinder contains so much pressure, when the valve opens, the gas is expelled with a violent force (that is why a vehicle without a muffler sounds so loud.)    The piston travels up to the top of the cylinder pushing all the exhaust out before closing the exhaust valve in preparation for starting the four stroke process over again.
Oiling System
Oil is the life-blood of the engine. An engine running without oil will last about as long as a human without blood. Oil is pumped under pressure to all the moving parts of the engine by an oil pump.  The oil pump is mounted at the bottom of the engine in the oil pan and is connected by a gear to either the crankshaft or the camshaft.  This way, when the engine is turning, the oil pump is pumping.  There is an oil pressure sensor near the oil pump that monitors pressure and sends this information to a warning light or a gauge on the dashboard. When you turn the ignition key on, but before you start the car, the oil light should light, indicating that there is no oil pressure yet, but also letting you know that the warning system is working.  As soon as you start cranking the engine to start it, the light should go out indicating that there is oil pressure.
Engine Cooling
Internal combustion engines must maintain a stable operating temperature, not too hot and not too cold.  With the massive amounts of heat that is generated from the combustion process, if the engine did not have a method for cooling itself, it would quickly self-destruct.  Major engine parts can warp causing oil and water leaks and the oil will boil and become useless. While some engines are air-cooled, the vast majority of engines are liquid cooled.   The water pump circulates coolant throughout the engine, hitting the hot areas around the cylinders and heads and then sends the hot coolant to the radiator to be cooled off.
Engine Balance
Flywheel:  A 4 cylinder engine produces a power stroke every half crankshaft revolution, an 8 cylinder, every quarter revolution.  This means that a V8 will be smother running than a 4.  To keep the combustion pulses from generating a vibration,  a flywheel is attached to the back of the crankshaft.  The flywheel is a disk that is about 12 to 15 inches in diameter. On a standard transmission car, the flywheel is a heavy iron disk that doubles as part of the clutch system. On automatic equipped vehicles, the flywheel is a stamped steel plate that mounts the heavy torque converter.  The flywheel uses inertia to smooth out the normal engine pulses.

Balance Shaft: Some engines have an inherent rocking motion that produces an annoying vibration while running.  To combat this,  engineers employ one or more balance shafts. A balance shaft is a heavy shaft that runs through the engine parallel to the crankshaft. This shaft has large weights that, while spinning, offset the rocking motion of  the engine by creating an opposite rocking motion of their own.

This content is provided to you by All Makes Automotive Services.

All-Makes is the place to go for all your auto repair needs in Rio Rancho, NM.