The radiator of a motor car is cooled by convection. When the engine is running, it produces heat that is transferred to the coolant fluid circulating through the engine block. This heated fluid then flows through the radiator, which is designed to dissipate the heat through the process of convection. In this process, the hot coolant transfers its heat to the metal fins of the radiator, which are in contact with the outside air. As the air flows over the fins, it absorbs the heat from the coolant and carries it away, cooling the engine. Radiation and conduction can also contribute to cooling, but the primary cooling mechanism for a car radiator is convection.