Engine Cooling System
Although gasoline engines have improved a lot, they are still not very efficient at turning gasoline into mechanical power. Most of the energy in the gasoline, about 70%, is converted into heat. The job of the cooling system is to take care of that heat. In fact, the cooling system on a car driving down the freeway dissipates enough heat to heat two average-sized houses!
The primary job of the cooling system is to keep the engine from overheating. This is done by transferring heat into the air. This is not the only job done by the cooling system; there are several other important jobs that it does.
The engine in your car runs best at a fairly high temperature. When the engine is cold, parts tend to wear out faster, and the engine is less efficient causing more pollution. So, another important job of the cooling system is to allow the engine to heat up as quickly as possible, and then to keep the engine at a constant temperature.
Liquid-cooled car engines have a small device called the thermostat which is between the engine and the radiator. The thermostat in most cars is about 2 inches in diameter. The job of the thermostat is to block the flow of coolant to the radiator until the engine has warmed up. When the engine is cold coolant does not flow through the engine. Once the engine reaches its operating temperature (about 200 degrees F), the thermostat opens. By letting the engine warm up as quickly as possible, the thermostat reduces engine wear, deposits and emissions.