The thermal switch turns on the fan at a certain coolant temperature. The switch should be checked if the fan does not turn on when the radiator is hot. Before checking the thermal switch, make sure that its wiring is in good condition (see Chapter On-board electrical equipment), as well as the thermostat and safety valve in the radiator cap. If any damage to these parts occurs, the thermal switch cannot operate, since it is not heated by the coolant.
The radiator fan can turn on automatically when the engine is off and the ignition is on (position "II" of the ignition key). Due to the heat removal processes taking place in the engine compartment, this can happen repeatedly. Therefore, if possible, the ignition should be turned off when working in the engine compartment.
1. Drain the coolant.
2. Disconnect the thermal switch connector. On petrol engines, the thermal switch is screwed into the radiator at the bottom near the right expansion tank of the cooling system, and on a diesel engine - at the bottom near the left expansion tank.
3. Unscrew the thermal switch.
4. Hang the thermal switch in a water bath and slowly heat the water.
Checking the ECT sensor
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5. Check the thermal switch circuit with an ohmmeter. No current should flow when the thermal switch is removed (resistance is infinite). When the switch is on, current should flow (resistance = 0 Ohm). When the thermal switch is turned on, a click should be clearly heard.
6. The thermal switch should turn on at a temperature of approximately 100 degrees.
7. Allow the liquid in the water bath to cool and check if the thermal switch trips at a temperature 95 degrees.
8. If the thermal switch does not meet the above parameters, it should be replaced.
9. Screw in the thermal switch with a new sealing ring with force 20 Nm.
10. Connect the electrical wiring.
11. To complete the installation, fill the cooling system and bleed air from it.
12. Warm up the engine and let it idle until the radiator fan comes on. Check the coolant level again.
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