Engine Coolant Thermostat - Operation

OPERATION

WARM-UP PHASE





Up to a coolant temperature of approximately 87° C (189° F), the main valve is closed and the bypass valve fully open. The flow through the radiator is interrupted and coolant flows through the bypass passage directly to the inlet side of the water pump.

PARTIAL-LOAD PHASE





The main valve begins to open at a coolant temperature of 86° C (189° F), and a small amount of coolant flows through the radiator. As the engine temperature increases, the main valve opens further and the bypass valve gradually closes. More coolant flows through the radiator and less coolant flows through the bypass passage.

FULL-LOAD PHASE





The main valve is fully open at a coolant temperature above 102° C (216° F). The bypass plate seals off the bypass passage. The entire quantity of coolant flows through the radiator.