Does any body know what is "FAN CLUTCH" and what is its job in bmw?

my bmw overheated couple days ago i brought it to a mechanic shop and he said the water pump leaking.i left the car there and the day after when i came there to pick up my car he said your fan clutch was damaged . he charged me 150 for changing the clutch and 250 for changing the water pump.but i don't know what is fan clutch.
Does any body know what is %26quot;FAN CLUTCH%26quot; and what is its job in bmw?
I'll try to explain. The belt turns the pulley on the front of the water pump, right? That's what pumps the coolant throughout your engine, heater, and radiator. Well right in front of that pulley is the fan clutch, then the fan is bolted to it.



When the engine is cool, it doesn't need the fan to spin at full speed, so the fan clutch allows it to spin freely. The fan will still spin a bit since it's not freespooling - just not locked up. If the engine is running and cold, you can hold the fan with your hand and make it stop spinning (Disclaimer: I don't recommend this). It takes some energy to turn the fast as fast as the engine due to the amount of air it's pushing, so it takes less energy (and, hence, gasoline) to run the engine without powering the fan.



There is a temperature-sensitive silicone-based fluid inside the fan clutch that gets thicker as the temperature goes up. So when the engine gets warmer, the fan clutch gradually becomes more resistant to spinning, so as the belt turns the water pump pulley, it's also turning the fan blade, sucking cool air through the radiator to keep your engine cool.
Does any body know what is %26quot;FAN CLUTCH%26quot; and what is its job in bmw?
Well since you didn't sat the model and year. You may or may not have been ripped off. If the clutch with the usual markup was worth say 140 bucks then no if it was the 100 clutch then yes. Model and year is important here. The fan clutch is removed anyways when a water pump job is done the only extra part is a few small bolts to bolt the clutch to the fan.

What a fan clutch does and how it works.

The fan clutch has silicone in it that reacts to temperature changes. A water pump pulley will spin at the same rate of speed as the engine does mostly there is a bit of RMP change with the pulleys sizes at the crank and at the water pump pulley. But its always the same. Now part of the fan clutch spins the same as the water pump but in the fan clutch there are bearings and the silicone I talked about earlier with this silicone in the clutch there is no solid mechanical connection from one side of the clutch to the other. The only connection is the bearings and the silicone. When the silicone is cold it is very watery but as it heats up if becomes thicker and thicker in turn creating a more solid connection as temperature goes up thus the fan clutch system begins to turn the fan with more force causing more and more air to be drawn thru the radiator removing heat from the coolant and blowing less hot air over the engine. This more solid connection never gets as strong as a true solid connection and you could if you wanted to stick your hand in the fan blade and not get hurt MUCH it may sting your finger a bit but no harm done.
Just like eric says the fan clutch is what the fan is mounted onto, this in turn is mounted to the drive of the water pump.



My guess from experience is that your mechanic had trouble getting it off and it got damaged but, if your engine has done a lot of miles then it is best all round that you have a new one anyway.




The clutch on your fan is a friction clutch device as it gats hot friction increases and your fan spins. Then when temps decrease the fan spins less.