The engine cooling system keeps the engine at its most efficient temperature at all speeds and operating conditions.  It consists of radiator, radiator pressure cap, coolant recovery tank, hoses, thermostat, water pump, fan and fan belt.  The water pump circulates the coolant from radiator through the passages surrounding the hot cylinders, combustion chambers and valves where the heat is transfered to the coolant.  The heated coolant then flows back to radiator through a hose.  When the coolant flows through the tube of the radiator, the heat is transferred to air.  The air is forced through the radiator passages by the fan and the car motion.

The thermostat is used to keep the engine at normal operating temperature.  It is an automatic valve to control the coolant circulation.  It closes when engine is cold and opens when engine is hot.

The coolant recovery tank is an expansion reservior.  When the engine heats up, the coolant expands and flows into the tank.  When the engine is turned off and cooled down, the coolant contracts and creates a partial vacuum to pull the coolant from the tank back into the radiator.  The radiator pressure cap severs as a valve to control this process.

The heater core is used to heat the passenger compartment.  It is just like a small "radiator".