System Operation: Notes

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. A separate circuit from the engine also feeds the heater core with coolant. The coolant pump, operated by engine rotation through the accessory drive belt, circulates the coolant. 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.

The transmission cooler - warmer is mounted on the transmission. On initial startup, the transmission fluid heater coolant control valve opens and allows warm coolant from the engine to enter the transmission cooler - warmer to warm the transmission fluid. As the engine and transmission warm, the transmission fluid heater coolant control valve closes and the transmission fluid cooler coolant control valve opens, allowing cooler coolant from the radiator to enter the transmission cooler - warmer to cool the transmission fluid.

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

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 sets, and the MIL  illuminates.