In general, one can define cooling as the reduction of temperature of an object or system due to heat extraction from it.
NECESSITY OF COOLING IN IC ENGINES:
Where as the energy generated during combustion of fuel inside the cylinder is the source of heat input Qf. Out of this energy, approximately one third part is converted into useful work, one third has been carried away by the hot exhaust gas. A part of the remaining one third fraction of the energy has been accounted for various losses including frictional power, where as the remaining portion of heat energy flows into cylinder, thus making it hotter. The cylinder itself radiates heat to air, but rate of heat leakage is very small compared to the heat energy the cylinder is receiving from hot gases. Therefore, the temperature of the cylinder will start to increase until it becomes so hot that