Thousands of automobiles are stranded on the side of the road due to cooling system problems each year. Precautions can be taken to avoid this, including paying attention to the temperature gauge. Engine coolant, in addition to oil, carries away excess heat from the engine. Too much heat can destroy an engine, while an engine that is not at the proper operating temperature will run inefficiently. This section will identify and discuss the importance of the cooling system, maintenance procedures, and cooling system component identification.
This engine warning light comes on when your engine has reached a potentially damaging temperature. Overheating an engine can warp and crack cylinder heads, overheat the engine oil, and cause excessive stress on engine components. If the temperature light stays on (or the gauge is in the HOT range), pull over to the side of the road and let the engine cool.
Purpose of the Cooling System
The cooling system is designed to do three things:
- Maintain efficient operating temperature.
- Remove excess engine heat.
- Reach operating temperature quickly.
Maintaining Operating Temperature
On today’s computer controlled vehicles it is vital to maintain an efficient operating temperature. Too low of a temperature will cause the computer to run the vehicle with a rich air-fuel mixture. Too high of a temperature and the engine will warp metal and crack gaskets, which could eventually lead to major engine damage. Most vehicles run coolant at a temperature of around 200 degrees Fahrenheit. Coolant temperature is controlled by a thermostat, which will be discussed later in this chapter.
- Coolant low
- Improper coolant mixture
- Clogged radiator fins
- Faulty thermostat (stuck closed)
- Restricted radiator hose
- Fan not working
- Faulty temperature sensor
- Faulty water pump
- Drive belt loose
- Faulty radiator cap
Removes Excess Heat
Temperatures of the metal around the combustion chamber (where the fuel is ignited) can reach extremely high temperatures. Coolant flows throughout the engine to remove this excess heat and transfer it to the radiator where it is eventually cooled.
Reach Operating Temperature
Gasoline is wasted every second the engine runs below the most efficient operating temperature. The electronic control module communicates with the temperature sensor and regulates the other systems based on the coolant temperature. An engine running at the proper temperature will run cleaner, smoother, and more efficient than an engine running too cool or too hot.
- Faulty thermostat (stuck open)
- Faulty temperature sensor
Cooling System Components
The following cooling system components will be discussed:
- Water Pump
- Radiator and Heater Hoses
- Radiator Cap
- Radiator Fan
- Drive Belts
- Coolant Recovery Tank
The water pump is attached to the engine block. Its main purpose is to keep the coolant circulating. It draws cooled coolant in from the lower radiator hose and pushes it through the engine. An engine drive belt (“v” or serpentine) rotates most water pumps.
The purpose of the radiator is to remove heat from the coolant. Hot coolant enters the radiator by the upper radiator hose when the temperature of the coolant reaches the opening rating of the thermostat. The coolant runs down through various tubes. Air is drawn around the radiator tubes by a fan and by the motion of the vehicle. The air flow cools the coolant in the radiator tubes so it can be returned to the engine.
The thermostat is the brain of the cooling system. It senses the temperature of the coolant and allows the fluid to exit to the radiator. The thermostat controls the temperature in the cooling system. Thermostats are rated at a specified temperature usually between 180 to 195 degrees Fahrenheit. When an engine is cold, the thermostat is closed. Once the engine temperature reaches the thermostat rating, the thermostat opens.
Two main hoses attach the radiator to the engine. These hoses are called the upper and lower radiator hoses. Cooled coolant is transferred from the radiator to the engine through the lower hose. Hot coolant is returned to the radiator by the upper hose. The upper hose usually connects to the water outlet that covers the thermostat. The lower hose connects to the water pump. Heater hoses are used to transport heated coolant to the heater core (basically a mini-radiator). The heater core is located on the engine compartment’s firewall. The heater fan, controlled by the operator, can blow air through the heater core providing heat inside the vehicle on cold days.
The radiator cap is designed to maintain a constant pressure in the cooling system. Most pressure caps are rated between 8 to 16 PSI. PSI stands for pounds per square inch. Increasing pressure on the cooling system also increases the boiling point of the coolant. The radiator cap allows expanding coolant to go to the coolant recovery tank. When the fluid has cooled, it is drawn back into the radiator.
Radiator fans draw air through the radiator to cool the coolant. Fans are either mechanically or electrically driven. A mechanical fan is driven by a belt. An electrical fan is driven by an electric motor. Most newer vehicles use an electric fan because it is more efficient and more suitable for front-wheel drive vehicles with transverse engines.
Drive belts turn water pumps, mechanical fans, power steering pumps, and air conditioning compressors. Automotive drive belts are connected to the crankshaft pulley that turns from the reciprocating motion of the engine. Worn or loose belts can cause slippage. Belt slippage can lead to an engine overheating.
Coolant Recovery Tank
The coolant recovery tank (also called the expansion bottle) holds excess coolant during the cooling system operation. As pressure and heat build up, the coolant expands and is then transferred to the recovery tank. This allows no fluid loss during cooling system operation, while keeping the maximum amount of coolant in the system at all times. Another advantage of using a coolant recovery tank is to keep outside air from being drawn into the engine block. Air, carrying in outside contaminants, can cause rust in cooling system components.
Mainly two types of coolant are sold for automotive use: standard antifreeze and extended life antifreeze. Standard antifreeze, green in color, was most commonly used in vehicles prior to 1995. Extended life coolants, such as Dex-Cool, are usually orange in color. Dex-Cool is a type of antifreeze common in 1995 and newer GM vehicles. As presented in Chapter 6, Fluid Level Check, antifreeze can come in various colors. Always refer to your owner’s manual to identify the correct antifreeze to use in your vehicle. Both standard antifreeze (green) and extended life antifreeze are ethylene glycol based, which is toxic. The main differences between standard and extended life antifreeze are the rust inhibitors and additives used. Recently some manufacturers started producing more environmentally friendly antifreeze products that are propylene glycol based. These products are not as harmful to pets, wildlife, or humans if accidentally ingested. Coolant within an engine does three main things:
- Prevents freezing and boiling.
- Lubricates the water pump.
- Inhibits corrosion.
Freezing and Boiling
Pure water should not be used to cool an engine. A couple of problems exist with using pure water. Water freezes at 32 degrees Fahrenheit and boils at 212 degrees Fahrenheit. Vehicles in some parts of the country are driven in temperatures below 32 degrees Fahrenheit. If coolant freezes, it will expand and eventually crack the engine block. Also, the engine can run hotter than 212 degrees Fahrenheit. If the coolant boils it causes problems. The solution to this is to use an antifreeze/water mixture. In most climates a 50% water to 50% antifreeze mixture is recommended. This will give the coolant a freezing point of 34 degrees Fahrenheit and a boiling point of about 225 degrees Fahrenheit. In a severely cold climate, 60% antifreeze to 40% water is necessary. It is not recommended to use pure antifreeze in the coolant system. The antifreeze/water mixture carries the best properties.
The coolant mixture lubricates bearings that are located inside the water pump. As antifreeze ages, its lubricating ability lessens.
Bare engine components are susceptible to corrosion. Coolant contains chemicals to minimize rust and corrosion from taking place inside the engine.
Used coolant is considered a hazardous waste. Bring the coolant to a service center that recycles it or wait until your community has a hazardous waste pickup day. If you have to store the coolant, do not leave it in open pans where pets or children can get into it.
The water pump causes coolant to flow throughout the engine. Coolant travels in passageways called water jackets. Coolant is moved from the radiator, through the lower radiator hose, to the water pump, to the numerous water jackets, to the thermostat, through the upper radiator hose, and back to the radiator. Coolant is separated from the engine oil and combustion chamber by gaskets and seals.
- Defective seal or gasket
- Hole in radiator
- Hole in hose
- Engine overheating and boiling over
- Loose hose clamp
The cooling system is extremely important to the operation of the engine. Without it, the engine block could actually melt. The three purposes of the cooling system are to maintain efficient engine-operating temperature, remove excess heat, and to bring the engine up to operating temperature as quickly as possible. Antifreeze prevents the coolant from freezing, increases the boiling temperature, lubricates components within the engine, and reduces the likelihood of corrosion.
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