Pos. | spare part no | Name |
A | - | Cooling system (temperate climate vehicles) |
B | - | Additional elements of the cooling system (cold climate vehicles) |
1 | - | FFBH |
2 | - | Additional coolant pump |
Cold engine
When starting the engine, the coolant pump is driven by the timing belt. It circulates coolant through the cylinder block, oil cooler and cylinder head. Coolant also flows through the climate control heater circuit and through the EGR heat exchanger. The thermostat is in the closed position and prevents the return of coolant from the engine to the radiator.
When the thermostat is closed, the bypass valve opens to direct the return coolant through the temperature control module and coolant manifold to the coolant pump housing. The coolant continues to circulate and is gradually heated by the engine. The gases present in the cooling system exit through the air outlet line of the temperature control module to the expansion tank.
An increase in coolant temperature is sensed in the thermostat and reflected in the coolant temperature gauge on the instrument cluster via the ECM and the ECT sensor signal.
For more information, see chapter: Instrument panel (413-01 Instrument panel, Description and function).
Normal engine operating temperature
As the coolant temperature rises at 83°C, the thermostat begins to react and open. The bypass valve gradually closes. Hot coolant returning from the engine to the temperature control module can now pass through the top hose to the radiator. The flow of hot coolant to the radiator now causes the cold coolant in the radiator and lower hose to flow to the temperature control module.
During the thermostat opening period, there is a primary coolant temperature difference on both sides of the thermostat. The thermostat reacts to the temperature difference and partially closes, while the bypass valve opens further. The thermostat and bypass valve continue to fluctuate as the coolant temperature increases.
At a coolant temperature of 91°C, the thermostat is fully open and the bypass valve is fully closed. Coolant returning from the engine now circulates completely through the radiator and bottom hose. The coolant flows through the radiator from the right reservoir to the left reservoir and is cooled by air passing through the radiator core. The gases present in the radiator exit through the air outlet line to the expansion tank.
The increase in coolant volume caused by thermal expansion causes the coolant level to rise through the reservoir connecting hose and the fluid enters the reservoir.
The temperature of the cooling system is continuously monitored by the ECM via the ECT sensor signal. The ECT signal is used by the ECM to control the operation of the cooling fans and regulate the fuel delivery. The ECM also controls the fans according to input from the automatic transmission fluid temperature sensor, the A/C control switch, and the A/C pressure sensor. For more information see the chapter: Electronic Engine Controls - 2.2L Diesel (303-14 Electronic Engine Controls - 2.2L Diesel, Description and function). For more information, see the chapter: Air conditioning (412-01 Climate control, Description and principle of operation).
In addition, the speed of the cooling fan depends on the speed of the vehicle. The ECM controls the speed of the cooling fans to compensate for the effect of ram air pressure. The road speed signal is transmitted via the CAN bus from the anti-lock brake system module (ABS).
When the engine is turned off, the temperature and volume of the coolant decrease. The thermostat starts to close as soon as the coolant temperature drops to 89°C and closes completely at 81°C. The coolant level in the reservoir decreases as coolant is drawn out of the reservoir to replenish the system.
After the engine is turned off with the water pump stationary, the ECM may continue to keep the cooling fans running for a pre-set period of time to keep the engine cool.
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