Can someone explain the normal operation of the cooling fan clutch?

[EricB]

I really do search the forums before asking these oddball questions, but this car seems to be different than other cars I've owned.

At idle, my cooling fan is barely moving, if at all.
It starts to turn at over 1000 rpms.

This doesn't seem right to me, but I'm not really having any overheating issues here in the dog days of the Arizona summer.

(I do sometimes hear a howl that I can only suspect is a belt slipping on something, but thats another issue I suspect)

What is it supposed to be like?

[Anton CH.]

On mine here is how it is:

With engine cold its easy to spin the fan around the engine
With engine hot I could feel a lot of resistance when spinning the fan
At idle the fan turns on its own

The fan is really there at low engine speed operation such as when you are sitting at a stop light with AC blasting on full. At high speeds you don't really need the fan.

[bmwrp8]

On mine here is how it is:

With engine cold its easy to spin the fan around the engine
With engine hot I could feel a lot of resistance when spinning the fan
At idle the fan turns on its own

The fan is really there at low engine speed operation such as when you are sitting at a stop light with AC blasting on full. At high speeds you don't really need the fan.

same here:)

[Podmore]

The fan should be spinning at pretty much engine rpm at idle and low speed; at high speed it should freewheel, thus reducing the load on the engine. As stated above, at speed the movement of the car is sufficient to puch enough air through the radiator for effective cooling. Therefore if your fan is not spinning at idle, you have a problem!

[Paul in NZ]

the clutch works as the temp rises,if the air comimg of the radiator is "hot" the clutch engages somewhat so spinning the fan at "belt speed"As the temperature lowers the fan disengages somewhat leavng the fan to nearly freewheel.If i am driving around town and lots od stop go as you accellerate and are surrounded by buildings and have the window down you can hear when the fn is engaged..your car( at least mine) sounds like an old truck..as soon as you get going and air begins to pass through the radiator the fan disengages and quiets down

[J.DeFeo]

On mine here is how it is:

With engine cold its easy to spin the fan around the engine
With engine hot I could feel a lot of resistance when spinning the fan
At idle the fan turns on its own

The fan is really there at low engine speed operation such as when you are sitting at a stop light with AC blasting on full. At high speeds you don't really need the fan.

So if the fan spins freely when the engine is hot, then the clutch is busted? I just fixed my aux fan and that helped a lot with my overheating problems but the temp needle still creeps above the 1/2 way point. I don't ever hear the fan clutch engaging, either.

[dennyg]

If your aux fan is working and your car is running hot then chances are its not working properly. With water temp above middle take a pop can and see if you can stop the fan. Don't stick it in too close cause its not something you want to touch with your hand lol. If the can stops the fan with out much resistance then its not working right. Mine just went out in rush hour traffic in Detroit (95 degree day too). One tip if its happening to you and you can't stop. Turn the heat on full.

[EricB]

Thanks for the answers.
I'm pretty sure that my fan clutch isn't working properly.

I popped the hood in the garage after driving home from work and the fan was rapidly decellerating down to a stop.

I had my wife step on the gas until up to about 2000 rpm and the fan started moving again, slowly.

So, $100 part right?

[Jon K]

So if the fan spins freely when the engine is hot, then the clutch is busted? I just fixed my aux fan and that helped a lot with my overheating problems but the temp needle still creeps above the 1/2 way point. I don't ever hear the fan clutch engaging, either.

Yeah if it spins freely hot, it's a goner. The radiator has very little to do with the fan cluthc - its a viscous coupler, and the friction of it spinning warms the oil inside it which it expands, etc. The fan is clutched so that high engine RPM the fan does not travel at engine rpm, else the fan would explode.

But yea cold start, if you ran the engine for a few secs and shut it off, the fan would take ~5 seconds to come to a stop. Run the car for about 5 mins and the fan should take about only 2 or so turns to stop.

[Tiger]

Yeah... sounds like you got a bad clutch. I got a spare clutch... it was new when I bought it long ago... thinking I will need it... but no... 7 years passed by... How about $75 shipped? It is OE BMW fan clutch.

[whiskychaser]

Hang on a mo. I posted a similar query only a couple of weeks ago. My understanding then was:

engine hot. at idle the fan should turn but not at belt speed
as revs are increased the clutch engages and there is a very noticeable increase in fan speed and much more air is blown back. If this doesnt happen the clutch has had it.

This is exactly how mine works. I actually get less resistance to turning the fan by hand after the motor has been run than when its cold.

[EricB]

PM Sent, Tiger.