components prematurely wear out. If the cooling system fails to keep the engine at the right
temperature, it can suffer significant damage and, in some cases, fail entirely.

Water Pump Although a few cars are air-cooled, most modern vehicles use liquid cooling. Here are the
critical components in liquid-cooled systems.

Coolant, or antifreeze, performs two critical functions. It keeps the radiator fluid from freezing in wintry
conditions and keeps the engine from overheating in warm weather. Coolant is composed of 50
percent ethylene glycol and 50 percent water, which helps raise its boiling point and lower its freezing
point. Corrosion inhibitors protect vital metallic cooling system components from corroding and
silicates lubricate seals. There are different kinds of antifreeze, which are most easily identified by
their color. How do they differ?

"The green stuff” is traditional coolant, which can be used in most cars. It contains lubricating silicates
and corrosion inhibitors, but these silicates deteriorate rather quickly, requiring coolant changes every
two years/24,000 miles.
Coolant can also be red, yellow, orange, or even purple. These coolants are pretty much the same;
they are simply dyed different colors. They have a longer claimed service life, thus requiring fewer
fluid changes—in some cases up to 100,000 miles. Refer to your owner’s manual for details on your
The radiator is a heat exchanger with hundreds of individual tubes and fins that reduce the
temperature of the coolant. As coolant travels through the engine passageways, it absorbs and
removes heat from the engine, transporting it to the radiator. Air flows through the coolant passages
as the car moves, cooling the tubes and fins, and coolant reenters the engine with a reduced

Radiator Cap
If you’ve ever worked on a car, then you know not to remove the radiator cap while the engine is
warm. That's because the cap is a pressure-release valve. It keeps the cooling system under pressure
in order to increase the boiling point of coolant.

Engine/Radiator Fan
The engine/radiator fan can be driven by a drive belt or an electric motor. It helps cool a car when it's
stationary or moving slowly.

The thermostat helps the engine reach operating temperature by preventing coolant from circulating
to the radiator, thus allowing the engine to heat up more quickly. As the engine reaches operating
temperature, the thermostat opens and allows coolant to flow through the radiator.

Water Pump
The water pump circulates coolant through the system via an impeller (a rotor that spins to move
fluid), which is driven by a belt.

Heater Core
The heater core is a smaller version of the radiator and located underneath the dashboard. A motor
blows air past the heater core, which transfers heat to the air. This keeps cabin occupants warm, even
in winter.

Transmission Cooler
In addition to keeping the engine cool, on cars with an automatic transmission, the radiator is
equipped with a separate heat exchanger to keep transmission fluid from boiling over.

If your car is leaking coolant, immediately determine from where and how much. If it continues to leak,
schedule your car for service as soon as possible
Heater Core
Radiator Hose - Lower
Radiator Hose - Upper
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