Heat is a form of energy that can be sensed by a change in temperature. The engine cooling system uses chemical energy in the fuel and converts it into heat and then into movement. The energy conversion process in an engine is not very efficient and only about 30% is converted into movement energy.
Of the remaining heat, up to 50% goes out of the exhaust and the rest heats the engine. Excessive heating of the engine must be controlled to prevent damage. Components expand with heat and, at high temperatures, this expansion can cause seizure, and burning of pistons and valve seats. High temperature would also produce rapid deterioration of the engine engine cooling system oil.
Cooling systems are designed to maintain engines at an optimum temperature. This allows the design of components that expand on heating to form very tight fits and running tolerances. The adjustment of ignition and fuel settings is equated to the optimum temperature required for the clean and efficient combustion of fuel. Because a cold engine produces high levels of unwanted exhaust emissions, a rapid warm-up is needed to keep missions to a minimum. The ‘normal’ running engine coolant temperature is maintained at about the boiling point of water, which enables efficient combustion. A further reduction in harmful exhaust emissions is achieved by keeping the warm-up time to a minimum. There are two types of cooling system.
Air-cooled systems have the air stream passing directly over the cylinder heads and cylinders to remove heat from the source . Fins are cast into the cylinder heads and cylinders to increase the surface area of the components, thus ensuring that sufficient heat is lost.
Liquid-cooling systems use a coolant to carry heat out of the engine and dissipate the heat into the passing air stream . The liquid coolant is contained in a closed system and is made to circulate almost continuously by the impeller on the water pump. Heat is collected in the engine and dissipated from the radiator into the passing air stream. Almost all modern cars and light vehicles use liquid cooling systems.