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General Motors just introduced a new five year, 100,000 mile antifreeze in its 1996 cars and light trucks. The new coolant is called "Dex-Cool" and is dyed orange to distinguish it from ordinary antifreeze (which is green).
CAUTION: These new long life coolants provide extended life only when used in a clean system mixed with water. If mixed with ordinary antifreeze and/or old coolant in a system, the corrosion protection is reduced to that of normal antifreeze (2 to 3 years and 30,000 miles).
CORROSION INHIBITORS
The life of the antifreeze depends on it's ability to inhibit corrosion. Silicates, phosphates and/or borates are used as corrosion inhibitors to keep the solution alkaline. As long as the antifreeze remains so, corrosion is held in check and there's no need to change the coolant. But as the corrosion inhibiting chemicals are used up over time, electrolytic corrosion starts to eat away at the metal inside the engine and radiator. Aluminum is especially vulnerable to corrosion and can turn to Swiss cheese rather quickly when conditions are right. Solder bloom can also form in copper\brass radiators causing leaks and restrictions. So changing the coolant periodically as preventative maintenance is a good way to prevent costly repairs.
The basic idea is to change the coolant before the corrosion inhibitors reach dangerously low levels. Following the OEM change recommendations is usually good enough to keep corrosion in check, but it may not always be the case. That's why more frequent changes may be recommended to minimize the risk of corrosion in bimetal engines and aluminum radiators.
CHECKING THE ANTIFREEZE
One way to find out if it's time to change the antifreeze is to test it. One of the best ways to do that is with a special antifreeze test strips that react to the pH (alkalinity) of the coolant and change color. If the test strip indicates a marginal or bad condition, the coolant should be changed.
CHANGING THE COOLANT
Reverse flushing is the best way to change the coolant because draining alone can leave as much as 30 to 50% of the old coolant in the engine block. Reverse flushing also helps dislodge deposits and scale which can interfere with good heat transfer.
The concentration of antifreeze in the coolant also needs to be checked prior to the onset of cold weather. A 50/50 mixture of antifreeze and water is recommended and will protect against freezing down to -34 degrees F and boilover protection to 263 degrees F.
CAUTION: Do not use more than 70% antifreeze, and never run straight water in the cooling system because it offers no corrosion, freezing or boilover protection.
ANTIFREEZE DISPOSAL & RECYCLING
Regardless of the type of antifreeze you use, it should be disposed of properly. Antifreeze is biodegradable but take some time to break down. Dumping used antifreeze into a storm sewer, ditch, creek or on the ground can contaminate ground water and kill plants and fish. What's more, used antifreeze picks up lead from solder in copper/brass radiators. Lead is a toxic heavy metal that can also cause pollution problems of its own.
Most areas prohibit ANY dumping of used coolant (sanitary or storm sewers). They also may not accept used antifreeze in a sealed container for landfill collection because eventually the container will leak its contents into the ground causing possible ground water contamination.
So how do you get rid of the stuff? You can take your vehicle to a garage or service facility that has a coolant recycling machine. The latter is the best choice because it eliminates the disposal problem altogether.
Coolant recycling machines work their magic by a variety of means. Some use filtration while others use a distillation process to remove the harmful contaminants from the old antifreeze. Corrosion inhibiting chemicals are then added to restore the coolant's corrosion protection. The auto makers have all approved coolant recycling as an effective means of eliminating coolant disposal problems, and each publishes a list of machines that meet their specifications. Recycled coolant must meet minimum standards of purity before it can be reused.
Answer: THERMOSTAT STUCK SHUT
The thermostat, which is usually located in a housing where the upper radiator hose connects to the engine, controls the operating temperature of the engine. It does this by blocking the flow of coolant from the engine to the radiator until the engine reaches a certain temperature (usually 190 to 195 degrees F.). When this temperature is reached, the thermostat opens and allows coolant to circulate from the engine to the radiator.
If the thermostat fails to open, which can happen due to mechanical failure or if a steam pocket forms under the thermostat due to incomplete filling of the cooling system or coolant loss, no coolant will circulate between the engine and radiator, and the engine will quickly overheat.
You can check for this condition by carefully touching the upper radiator hose when the engine is first started and is warming up. If the upper radiator hose does not become hot to the touch within several minutes after starting the engine, it means the thermostat is probably defective and needs to be replaced.
CAUTION: The replacement thermostat should always have the same temperature rating as the original. Do not substitute a colder or hotter thermostat on any vehicle that has computerized engine controls as engine operating temperature affects the operation of the fuel, ignition and emissions control systems.
DEFECTIVE FAN CLUTCH
On rear wheel drive vehicles with belt-driven cooling fan, a "fan clutch" is often used to improve fuel economy. The clutch is a viscous-coupling filled with silicone oil. The clutch allows the fan to slip at high speed, which reduces the parasitic horsepower drag on the engine. If the clutch slips too much, however, the fan may not turn fast enough to keep the engine cool.
The silicone fluid inside the clutch breaks down over time and can leak out due to wear, too. If you see oily streaks radiating outward on the clutch (and/or the fan can be spun by hand with little or no resistance when the engine is off), it means the clutch is bad and needs to be replaced. Any play or wobble in the fan due to wear in the clutch also signals the need for a new clutch.
INOPERATIVE FAN MOTOR
On most front-wheel drive cars, the fan that cools the radiator is driven by an electric motor. A temperature switch or coolant sensor on the engine cycles the fan on and off as additional cooling is needed. If the temperature switch or coolant sensor (or the relay that routes power to the fan motor is bad), the fan won't come on when it is needed and the engine will overheat. Likewise, if the fan motor itself is bad, the fan won't work.
The system needs to be diagnosed to determine where the problem is so the correct component can be replaced.
EXTERNAL COOLANT LEAKS
Leaks in radiator or heater hoses, the water pump, radiator, heater core or engine freeze plugs can allow coolant to escape. No engine can tolerate the loss of coolant for very long, so it usually overheats as soon as a leak develops.
A visual inspection of the cooling system and engine will usually reveal where the coolant is going.
Leaks in hoses can only be fixed by replacing the hose. Leaks in the water pump also require replacing the pump. But leaks in a radiator, heater hose or freeze plug may sometimes respond to a sealer added to the cooling system.
WEAK OR LEAKY RADIATOR CAP
If no leaks are apparent, the radiator cap should be pressure tested to make sure it is holding the specified pressure. If the spring inside the cap is weak (or the cap is the wrong one for the application), the engine will lose coolant out the overflow tube every time it gets hot.
INTERNAL COOLANT LEAK
If there are no visible coolant leaks, but the engine is using coolant, there may be a crack in the cylinder head or block, or a leaky head gasket that is allowing coolant to escape into the combustion chamber or crankcase.
EXHAUST RESTRICTION
In some instances a severe exhaust restriction can produce enough backpressure to cause an engine to overheat. The most likely cause of the blockage would be a plugged catalytic converter or a crushed or damaged pipe. Checking intake vacuum and/or exhaust backpressure can diagnose this kind of problem.
BAD WATER PUMP
In a high mileage engine, the impeller that pumps the coolant through the engine inside the water pump may be so badly corroded that the blades are loose or eaten away. If such is the case, the pump must be replaced.
Most pump failures, however, occur at the pump shaft bearing and seal. After tens of thousands of miles of operation, the bearing and seal wear out. Coolant starts to leak out past the shaft seal, which may cause the engine to overheat due to the loss of coolant. A sealer additive will not stop this kind of leak. Replacing the water pump is the only cure.
CAUTION: A leaky water pump should be replaced without delay, not only to reduce the risk of engine overheating but to prevent catastrophic pump failure. If the shaft breaks on a rear-wheel drive vehicle, the fan may go forward and chew into the radiator ruining the radiator.
In rare instances, coolant may also leak into the automatic transmission fluid cooler if one is located inside the radiator. But usually when automatic transmission fluid leaks into the coolant it means the line is leaking.
Pressure testing the cooling system is necessary to diagnose an internal leak. A "cylinder leak-down test" can tell a mechanic if the coolant leak is in the combustion chamber. But to pinpoint an internal leak, it is usually necessary to remove the head(s) from the engine. The head may then be pressure tested and/or checked for cracks using special equipment.
Minor internal leaks can sometimes be temporarily sealed by adding a sealer to the cooling system. But large leaks or ones that do not respond to a sealer will have to be fixed.
If the problem is a cracked head or block, repairs may or may not be possible depending on the nature of the crack. Cracks in aluminum can often be repaired by welding while those in cast iron can be fixed by pinning the damaged area. But some cracks may be so bad that they are beyond repair or in a location that makes repair impossible. In such cases, the head or block must be replaced.
If a leaky head gasket is the culprit, replacing the gasket may only temporarily cure the problem if the head or block is warped. The mating surfaces on both the head and block should be checked for flatness and resurfaced if necessary to restore flatness for a proper seal.
The whole idea behind preventative maintenance is to replace things BEFORE they fail -- ideally just as the component is nearing the end of its normal service. Unfortunately, it's difficult to tell exactly when that point is reached. The original equipment radiator and heater hoses on some vehicles may go eight or ten years without a problem. Then again, they might not.
If your vehicle is more than eight years old and the hoses have never been replaced, you're probably driving on borrowed time. Replacing the hoses would be highly recommended if you're at all concerned about reliable transportation.
UNDERSTANDING HOSE FAILURES
Regardless of how frequently (or infrequently, if ever) the hoses are replaced, they should be inspected periodically to check for problems. Any hose that is leaking, age cracked, hard, brittle, mushy-feeling, bulging or otherwise damaged needs to be replaced.
Heat, vibration and internal corrosion are the factors that age the rubber in hoses and eventually make them fail. In many instances, a hose that looks good as new on the outside will be rotten on the inside. This is caused by "electrochemical degradation," and it occurs because the hose, coolant and metal parts of the cooling system form a galvanic cell or battery. The electrochemical reaction that results forms small micro cracks inside the hoses. The cracks allow coolant to penetrate the rubber and weaken the reinforcement. Heat and flexing accelerate the process, and eventually the hose fails from the inside out. The process may take years to occur, or it may happen in a relatively short time (25,000 miles or less) depending on the conditions that are present.
Upper radiator hoses and small diameter bypass hoses tend to be much more vulnerable to this type of internal failure than other hoses. One reason is because these hoses usually carry the hottest coolant. The smaller inside diameter of bypass hoses also seems to accelerate because the coolant is flowing through it at a higher velocity.
The opening of the thermostat allows coolant to circulate through the engine and cooling system. As the temperature of the coolant begins to drop, the wax element cools off and contracts allowing the thermostat to partially or fully close. Thus, by cycling open and shut a relatively constant operating temperature is maintained.
THERMOSTAT FAILURE
The thermostat is pretty simple and rarely causes problems, but when it fails the results can be disastrous. The worst case scenario is when the thermostat sticks shut, which can happen if the wax element has been damaged by previous overheating, corrosion or age. If it sticks shut, it will block the circulation of coolant between the engine and radiator causing the engine to overheat.
If the thermostat fails to close, which can happen if the sensing element binds up, the return spring breaks or a piece of rust or debris jams it open, the constant flow of coolant through the thermostat will prevent the engine from reaching normal operating temperature. This can cause poor driveability in cold weather, a sharp increase in fuel consumption, little or no heater output, and accelerated blowby and ring and cylinder wear.
THERMOSTAT CHECKS
To check the thermostat, remove the radiator cap and start the engine while it is cold. (CAUTION: NEVER REMOVE A RADIATIOR CAP WHEN THE ENGINE IS HOT OR THE RADIATOR TOP IS HOT OR THE UPPER RADIATIOR HOSE IS HOT!) Looking inside the radiator, you should see no movement of coolant. If you see movement, the thermostat is stuck open or is missing and repairs are required.
After the engine has run for five minutes or so, the upper radiator hose should start to feel hot signaling that the thermostat has opened and the coolant is now circulating through the system. Inside the radiator, you should also see coolant movement. If there is no movement (and the engine starts to overheat), the thermostat is defective and needs to be replaced.
A suspicious thermostat can also be tested by removing it from the engine and dropping it into a bucket of near boiling water. It should be closed when cold, then open once it hits the hot water, then close again after its been removed and allowed to cool. You can use a thermometer to check the exact opening and closing temperature.
Coolant temperature is used for a variety of engine and emission control functions. The coolant sensor on late model engines tells the computer when the engine has reached normal operating temperature. This, in turn, affects fuel enrichment, spark timing, operation of the EGR valve, purging of the charcoal canister, etc. Even on many non-computer engines, thermal vacuum switches (TVS) that react to a specific coolant temperature are used to open and close various vacuum circuits that regulate fuel enrichment, timing and emissions.
If a colder thermostat is installed, the coolant may never get hot enough to trigger the appropriate control functions in the computer or TVS vacuum circuits. As a result the engine will run as if it were continually cold, which increases both fuel consumption and emissions. Too low an operating temperature also increases cylinder wear.
CAUTION: Under no circumstances should an engine be driven without a thermostat! This can produce thermal stress that may crack a head or block!
What about a hotter thermostat? A hotter than normal thermostat in a late model computer controlled engine may activate some control functions too quickly or out of sequence with other control devices (timer delays, etc.) --which could also have an adverse effect on driveability, fuel economy, performance and emissions.
Electric cooling fans are found on most front-wheel drive vehicles with transverse mounted engines as well as many late model rear-wheel drive vehicles. Electric fans are used on FWD cars because the fan doesn't require a belt drive and can be mounted independent of the engine's location. What's more, electric fans require less power to operate (for improved fuel economy and performance), they're quieter, and they allow more precise control over cooling.
By comparison, a mechanical belt-driven fan can require anywhere from 5 to 15 horsepower depending on engine speed and the size of the fan. Even with a fan clutch to reduce the drag at higher speeds, it's still a lot of wasted power.
FAN OPERATION
At highway speeds, there is usually enough airflow through the radiator that a fan isn't needed. So the fan usually only operates when the vehicle is sitting in traffic or driving at slower speeds.
On older applications, the electric fan is controlled by a temperature switch located in the radiator or engine. When the temperature of the coolant exceeds the switch's rating (typically 195 to 235 degrees F), the switch closes and energizes a relay that supplies voltage to run the fan. The fan then continues to run until the coolant temperature drops back below the opening point of the switch. Most electric fans are also wired to come on when the A/C is on. Many vehicles also have a separate fan for the A/C condenser (dual fan systems). One or both fans come on when the A/C is on.
In newer vehicles with computerized engine controls, fan operation is regulated by the engine control module. Input from the coolant sensor, and in many cases the vehicle speed sensor too, is used to determine when the fan needs to be on.
CAUTION: Many electric fans are wired to come on anytime the engine is above a certain temperature, regardless of whether the engine is running or not. This means the fan may come on after the engine has been shut off. So keep your fingers away from the fan at all times unless the battery or fan motor wires have been disconnected.
CHECKING THE FAN
Four things can prevent a fan from coming on when it should: a bad temperature switch or coolant sensor (or problem in the switch or sensor wiring circuit); a bad fan relay; a wiring problem (blown fuse, loose or corroded connector, shorts, opens, etc.); or a failure of the fan motor itself. Only the latter would require replacing the fan motor.
One way to check the operation of the fan motor is to jump it directly to the battery. If it spins, the motor is good, and the problem is elsewhere in the wiring or control circuit. Another check is to test for voltage with a voltmeter or test light at the fan's wiring connector. There should be voltage when the engine is hot and when the A/C is on.