| Pos. | Spare part number | Name |
| A | - | Cooling system (vehicles for moderate climates) |
| B | - | Additional cooling system components (vehicles for cold climates) |
| 1 | - | FFBH |
| 2 | - | Additional coolant pump |
Cold engine
When the engine is started, the coolant pump is driven by the timing belt. It circulates coolant through the cylinder block, oil cooler and cylinder head. Coolant also passes through the climate control system heater circuit and through the EGR heat exchanger. The thermostat is in the closed position and prevents coolant from returning from the engine to the radiator.
When the thermostat is closed, the bypass valve opens, directing the returning 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. Gases present in the cooling system exit through the temperature control module air outlet line to the expansion tank.
The increase in coolant temperature is sensed by the thermostat and reflected on the coolant temperature gauge in the instrument cluster via the ECM and the ECT sensor signal.
For more information, refer to the chapter: Instrument cluster (413-01 Instrument cluster, Description and operating principle).
Normal engine operating temperature
As the coolant temperature increases at 83°C, the thermostat begins to react and open. The bypass valve gradually closes. The hot coolant returning from the engine to the thermal control module is now able to flow through the upper hose to the radiator. The flow of hot coolant to the radiator now forces the cold coolant in the radiator and lower hose to flow to the thermal control module.
During the thermostat opening period, there is an initial coolant temperature differential on both sides of the thermostat. The thermostat responds to the temperature differential and partially closes while the bypass valve opens further. The thermostat and bypass valve continue to oscillate as the coolant temperature increases.
(The source of the article is located on the website LRMAN.ru)
At 91°C the thermostat is fully open and the bypass valve is fully closed. The coolant returning from the engine is now fully circulated through the radiator and the lower hose. The coolant passes through the radiator from the right tank to the left tank and is cooled by the air passing through the radiator core. The gases present in the radiator are released 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 then enters the reservoir.
The cooling system temperature is continuously monitored by the ECM via the ECT sensor signal. The ECT signal is used by the ECM to control the cooling fans and regulate fuel delivery. The ECM also controls the fans based on input signals from the automatic transmission fluid temperature sensor, the air conditioning control switch, and the air conditioning 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).
In addition, the rotation speed of the cooling fan depends on the vehicle speed. The ECM regulates the rotation speed of the cooling fans to compensate for the effect of the air flow. The speed signal is transmitted via the CAN bus from the anti-lock brake system (ABS) module.
When the engine is turned off, the coolant temperature and volume decrease. The thermostat begins to close as soon as the coolant temperature decreases to 89°C and closes completely at 81°C. The coolant level in the reservoir decreases as coolant is drawn from the reservoir to replenish the system.
After the engine is turned off and the coolant pump is stationary, the ECM may continue to keep the cooling fans running for a preset period of time to maintain engine cooling.
Comments on this article