Description And Operation: Operation
COOLANT CIRCUIT FLOW
When the engine is running, the coolant is circulated around the engine cooling system by the coolant pump. From the coolant pump, coolant flows through the cylinder heads and the engine oil cooler into the cylinder block and the heater manifold.
In the cylinder block, the coolant flows forwards to the outlet tube. When the coolant is cold, the thermostat is closed and the coolant flows direct from the outlet tube back to the coolant pump. Once the coolant reaches operating temperature the thermostat begins to open, to control system temperature, and coolant flows from the outlet tube to the coolant pump via the radiator. When the thermostat is open, the coolant flow through the radiator also generates a coolant flow through the ATF cooler.
From the heater manifold the coolant flows through the throttle body and the heater core, in parallel circuits that are unaffected by the position of the thermostat. From the throttle body, the coolant merges with bleed coolant from the coolant pump and the outlet tube and flows to the expansion tank. From the heater core, the coolant flows back to the inlet of the coolant pump.
Expansion and contraction of the coolant is accommodated by an air space in the expansion tank and the compliance of the flexible hoses.
Engine Cooling Flow Diagram
| ITEM | DESCRIPTION |
|---|---|
| 1 | Expansion tank |
| 2 | Bleed screw |
| 3 | Heater core |
| 4 | Bleed screw |
| 5 | Cylinder head - Bank 1 |
| 6 | Cylinder block |
| 7 | Throttle body |
| 8 | Engine oil cooler |
| 9 | Heater manifold |
| 10 | Cylinder head - Bank 2 |
| 11 | Automatic Transmission Fluid (ATF) cooler |
| 12 | Check valve |
| 13 | Electric thermostat |
| 14 | Radiator |
| 15 | Coolant pump |
| 16 | Connections to charge air coolers |
THERMOSTAT
The thermostat begins to open (with ambient temperatures of 15-35°C (59-95 °F)) at 98-102 °C (208-215 °F) and is fully open at 108 °C (226 °F).
COOLANT LEVEL SENSOR
If the coolant level in the expansion tank decreases below a predetermined value, the coolant level sensor connects a ground to the CJB (Central Junction Box), which sends a message to the IC (Instrument Cluster) on the MS (Medium Speed) CAN (Controller Area Network) bus to display a warning message.
VISCOUS COOLING FAN
The ECM determines when to operate the cooling fan from the ECT (Engine Coolant Temperature) sensor input and a cooling fan request CAN bus message from the ATCM (Automatic Temperature Control Module). The ATCM sends the message on the MS CAN bus to the GWM (Gateway Module), which converts and transmits the message to the ECM via the HS CAN bus. The ECM also adjusts the fan speed to compensate for the ram effect of vehicle speed.
Viscous Cooling Fan
To control the viscous cooling fan, the ECM sends a PWM signal to the VCFCM. The ECM varies the duty cycle of the PWM signal between 0 and 100% to vary the clutch engagement and thus fan speed. If the PWM signal is outside the 0 to 100% range, the VCFCM interprets the signal as an open or short circuit and runs the fan at minimum speed to ensure the fan does not overspeed.
If the electrical connections to the viscous fan are disconnected the fan will idle and the engine may overheat. If ECM detects a cooling fan fault it stores the appropriate DTC (Diagnostic Trouble Code) and signals the IC on the HS CAN bus to display a warning message.