Engine Coolant Circuit Flow

When the engine is running, the variable coolant pump circulates the engine coolant through the engine cooling system.

At engine start up, the shroud of the variable coolant pump is partially shrouded. The variable coolant pump limits coolant flow in the engine cooling system. When required, the HVAC control module can request the variable coolant pump shroud to open to provide additional flow of the engine coolant.

When the engine coolant is cold, the electric thermostat is closed. This forces coolant through the bypass route back to the variable coolant pump.

When the engine coolant reaches operating temperature, the electric thermostat begins to open. The engine coolant flows through both the bypass route and radiator system to provide the required engine cooling.

When the electric thermostat is fully open, the majority of the engine coolant is directed through the radiator and the Automatic Transmission Fluid (ATF) cooler.

Expansion and contraction of the engine coolant is accommodated by an air space in the coolant expansion tank and the compliance of the flexible hoses.