Principles of Operation

Engine coolant flows primarily from the engine to the radiator circuit and back to the coolant pump. Coolant is sent from the coolant pump through the engine block and cylinder heads. Separate circuits from the engine also feed the heater core and turbochargers (if equipped) with coolant. The coolant pump circulates the coolant. For 3.5L Ti-VCT, 3.7L Ti-VCT and 3.5L GTDI engines, the coolant pump is operated by engine rotation through the timing chain sprocket. For 2.0L GTDI engines, the coolant pump is operated by engine rotation through the accessory drive belt pulley. The coolant thermostat is a control valve actuated by coolant temperature. When the thermostat is closed, coolant flow bypasses the radiator circuit and returns to the coolant pump. When the thermostat is opened, coolant flows through the radiator circuit to transfer engine-generated heat to the outside air.

For 2.0L GTDI engines, the transmission fluid cooler - warmer is mounted on top of the transmission. On initial startup, the temperature control valve bypasses the transmission fluid cooler - warmer circuit, and the coolant flows back to the engine. If the coolant is not extremely cold (above -9 °C [15 °F]), the temperature control valve directs coolant to the transmission fluid cooler - warmer circuit when the transmission is shifted to any gear other than park or neutral.

The degas bottle removes air from the cooling system, allows for coolant expansion and system pressurization, replenishes coolant to the cooling system and serves as the location for service fill.

The cooling fan draws air through the radiator to help cool the system coolant as it passes through the radiator.

The thermostat monitor is a function of the PCM and is designed to verify correct thermostat operation. The monitor executes once per drive cycle and has a monitor run duration of 300-800 seconds. If a malfunction occurs, DTC P0125 or P0128 is set, and the Malfunction Indicator Lamp (MIL) illuminates.

For the coolant flow diagrams, refer to Engine Cooling  in the Description and Operation portion of this article.