Remove thermostat.
Hang the thermostat in a container with water, heat the water.
Check if the valve rises from its place when heated to the specified temperatures.
If possible, also measure the valve travel.
Instruction. Thermostats after August 1978 are not recommended for older vehicles because the radiator fan thermostat, temperature sensor and gauge on the instrument panel are not adapted to the higher temperature.
Year of issue | Start of opening | End of opening | Valve travel minimum |
until July 1978 | around 80°C | around 94°C | 7 mm |
after August 1978 | around 87°C | about 102°С | 7 mm |
Malfunctions in the thermostat
characteristic feature | Cause |
The temperature display slowly rises; operating temperature is reached later than usual; insufficient heating | Thermostat valve locked in position "Offen" ("Open") due to pollution. The inflow to the radiator is constantly open. The engine does not reach operating temperature. But it doesn't cause damage. Despite this, the thermostat should be replaced soon |
The arrow of the temperature gauge is in the red area or completely to the right; The coolant overheat warning light flickers despite the level being correct. Radiator and bottom hose leading to radiator cold | Thermostat valve locked in position "Gesch Possen" ("Closed") due to a defective or leaky thermostat bushing. Never drive any further, otherwise the engine will be severely damaged. Replace thermostat |
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