Engine Cooling System: Operation

When engine is cold the thermostat is closed. The cooling system has no flow through the radiator. The coolant flows through the engine, water pump, and heater.
When engine is warm, the thermostat is full open. The coolant flows through the engine, radiator, heater, and water pump.
On the diesel engine coolant flows through the engine, radiator, heater, and water pump.
As coolant expands, some coolant will move to the coolant recovery container. Once the coolant cools, the coolant from the coolant recovery container will move back to the radiator. (Gas engine only)