A pellet-type thermostat in the coolant outlet passage controls the flow of the engine coolant. This allows proper engine warm-up and regulates coolant temperature. A wax pellet element in the thermostat expands when heated and contracts when cooled. The pellet connects through a piston to a valve. When the pellet heats, the valve opens. As the pellet cools, the contraction allows a spring to close the valve. The valve remains closed while the coolant is cold. This prevents circulation of coolant through the radiator.

When the engine warms and the thermostat valve opens, coolant flows through the radiator. in the radiator, heat is exchanged through the radiator into the surrounding air. This opening and closing of the thermostat permits enough coolant to enter the radiator in order to keep the engine within operating limits.