Before you go changing that sensor, please test it first! If it's stuck closed, the auxiliary fan will run continuously, even when the engine is cold. It can be identified by looking for a brass sensor with green plastic in the center...also has two plugs going to it. On the 560 engine (M117) the sensor is at the front of the engine, slightly to the passenger side.

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All the best,

J. P. Mose
1968 250SL
1970 280SE 3.5 Cabrio
1987 560SL
1990 560SEL