Entrained gases in the cooling system escape through the thermal control module degas line to the coolant reservoir.
The increasing coolant temperature is felt at the thermostat, and is registered on the instrument cluster coolant
temperature gage via the ECM and ECT sensor signal.
For additional information, refer to:
Instrument Cluster
(413-01 Instrument Cluster, Description and Operation).
Engine Normal Operating Temperature
With the coolant temperature increasing, at 83°C (181°F) the thermostat reacts and commences opening. The by-pass
valve is progressively closed. Hot coolant returning from the engine to the thermal control module is now allowed to pass
through the top hose connection to the radiator. The flow of hot coolant to the radiator now forces cold coolant within the
radiator and bottom hose to flow to the thermal control module.
During the thermostat opening period there is an initial temperature differential of the coolant at both sides of the
thermostat. The thermostat reacts to the temperature differential and partially closes, while the by-pass valve opens
further. The thermostat and by-pass valve continue to oscillate while the coolant temperature increases.
At a coolant temperature of 91°C (196°F) the thermostat is fully opened and the by-pass valve is fully closed. The return
coolant from the engine is now fully circulated through the radiator and bottom hose. Coolant flows through the radiator
from the RH tank to the LH tank, and is cooled by air passing through the matrix. Entrained gases in the radiator escape
through the connected degas line to the coolant reservoir.
The increased coolant volume created by heat expansion causes the coolant level to rise through the connecting reservoir
hose, and into the reservoir.
The temperature of the cooling system is constantly monitored by the ECM via the ECT sensor signal. The ECM uses the
ECT signal to control operation of the cooling fans, and to adjust engine fueling. The ECM also operates the fans in
response to inputs from the automatic transmission oil temperature sensor, Air Conditioning (A/C) system control switch,
and the A/C pressure sensor. For additional information, refer to: Electronic Engine Controls - 2.2L Diesel (303-14
Electronic Engine Controls - 2.2L Diesel, Description and Operation).
For additional information, refer to:
Air Conditioning
(412-01 Climate Control, Description and Operation).
The cooling fan speed is also influenced by vehicle road speed. The ECM adjusts the speed of the cooling fans to
compensate for the ram air effect, using the CAN bus road speed signal received from the Anti-Lock Brake System (ABS)
module.
When the engine is shut down, the coolant temperature and volume decrease. The thermostat starts to close as the
coolant temperature decreases to 89°C (192°F), and is fully closed at 81°C (178°F). The coolant level within the reservoir
decreases as coolant is drawn from the reservoir to replenish the system.
Following engine shut down when the coolant pump is stationary, the ECM may continue to operate the cooling fans for a
pre-determined period to maintain engine cooling.