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1984 300D
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9 Posts
Discussion Starter #1
Hello all,
I have a 1984 300D and I am wondering the proper operation of the fan and clutch and how to test it. A friend said the clutch was faulty because the fan turned continuously even when the engine was cold and just started. I purchased a new clutch and he installed it. The fan still turns from the start of a cold engine and I do not notice any difference in speed for ten minutes of operation. I am wondering how these things work and how can i test the one I just bought. I do not want to have to buy another one if there could be something else that is wrong. My coolant gauge works on the dash so I figure the sensor works. Any help is greatly appreciated.
 

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1979 & 1985 300D's
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2,537 Posts
My understanding is that these cars have fans that always turn. The clutch engages more at a given temperature to provide more air flow and releases more as the car cools again but it never stops.
 

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1978 mercedes 300D "silver streak" 2000 Mercedes ML320 1994 W124 Mercedes e500
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41 Posts
The fans always turn no matter how cold the engine is, since they're driven off the engine pulley and not electric like some cars which would enable it to stop and start seamlessly. The only thing that changes is how fast it spins, it has a bimetallic strip on it and when this gets hot enough (I believe it's around 73C) it changes shape and causes it to slip less and the fan to as a result, spin faster... At cold it's 2100rpm and max is 3200rpm (I think)


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1984 300D
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9 Posts
Discussion Starter #4
Thanks, I got conflicting info from the Mercedes service department. They said it should not turn when the engine is cold. They must have confused the older technology because they were suggesting checking the sensors. Thanks again
 
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