Remove the thermostat.
Hang the thermostat in a container with water and heat the water.
Check whether the valve lifts from its place when heated to the specified temperatures.
If possible, also measure the valve stroke.
Note: Thermostats used after August 1978 are not recommended for installation in older vehicles as the radiator fan thermostat switch, temperature sensor and instrument panel gauge are not designed for higher temperatures.
The original article is available at vwmanual.ru
| Year of issue | Beginning of the opening | End of opening | The valve stroke is minimal |
| until July 1978. | about 80°C | about 94°C | 7 mm |
| after August 1978. | about 87°C | about 102°C | 7 mm |
Thermostat malfunctions
| Characteristic feature | Cause |
| The temperature reading is slowly increasing; operating temperature is reached later than usual; insufficient heating | The thermostat valve is blocked in the "Off" position due to contamination. The inflow to the radiator is constantly open. The engine does not reach operating temperature. But this does not cause damage. Despite this, the thermostat should be replaced soon |
| The temperature gauge arrow is in the red area or to the right; the coolant overheating warning light is flashing even though the level is normal. The radiator and lower hose leading to the radiator are cold | Thermostat valve is stuck in position "Gesch Possen" ("Closed") due to a defective or leaky thermostat bushing. Do not drive any further under any circumstances, otherwise the engine will be severely damaged. Replace the thermostat |
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