Mercedes Benz repair: Fan Clutch Troubleshooting, clutch fan, fan clutch

Question
I have an 85 300d, its starting to run a little hot all of a sudden, i changed the thermostat, flush the system, how would i check the fan clutch for proper operation?

Answer
The viscous clutch can fail in two ways. One, the fluid that is inside the fan can run out and render the fan useless. Second, the bearing in the fan can fail and it will start making a lot of noise. If it is working properly it will make a whiring sound when the car gets warm You will really hear the fan working. When the car is cold you will not hear the sound at all. If you suspect the clutch fan is bad it is best to replace the unit. They are a little pricey (175.00)but is worth the money.