Mercedes-Benz W204 diesel not warming up or temperature gauge fluctuating
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Mercedes-Benz W204 diesel does not reach normal temperature, what is wrong?
A common cause is a thermostat that keeps the coolant circulation open. When the temperature stayed at about 75 degrees in freezing weather, a new thermostat raised it to about 90 degrees. In winter warming up normally takes about 10–20 km of driving, longer in city driving. The radiator must not be covered.
Mercedes-Benz W204 diesel: the temperature gauge swings between 80 and 115 degrees, what is the cause?
The cause varies from car to car. The gauge swinging has been fixed either by replacing the coolant temperature sensor or by reconnecting a loose fan wire. If replacing the sensor does not help, check the fan wire. A small swing between 80 and 90 degrees while driving is normal.
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