To dissipate the heat, coolant liquid which is usually water mixed with antifreeze , is circulated through cooling passage. In water cooling system, engine block and cylinder head have interconnected cooling channels. A pump driven by pulley and belt from crankshaft drives hot coolant out of the engine, to radiator, a heat exchanger. The radiator removes unwanted heat into air stream and the coolant liquid flows back to the channel. The radiator is linked to the engine by a rubber hose.
The system maintains the correct engine temperature irrespective of the outside temperature and the thermostat remains open as long as to keep engine at its optimum temperature.