Engine/Transmission (1998.5 - 2002) Fan clutch operation

[lfwood]

I have been getting a sporadic, but increasing frequency, elevated droning with vibration that increases with engine speed, regardless if moving or sitting stationary. There has also been a new whine, not unlike a bearing whine. Originally, I thought this to be coming from the exhaust system, but that has checked out. No leaks and the turbo is fine.



The problem has been getting worse and more frequent. I've had it into two service facilities, and they have not been able to isolate it.



Tonight, I thought to look at the fan behavoir. The engine was cold. When I started it, the fan came on quite forceful. It stayed that way until I shut down after several minutes and the fan stopped rotating abruptly with the engine. When I started/stopped it again, the same thing happened. The third through fifth start/stop cycles, the fan continued spinning free for some time. The sixth and last time, it stopped abrubtly.



For a cold engine, this fan clutch behavoir seems like I'm on to my problem. I should not, I think, have this much air volume being blown on a cold engine. Also, when shut off, there is a viscous resistance to manually rotating the blades for the first three revs, and then it will suddenly spin freely.



I took a side look to see if there was a wobble in the fan, but with the speed of rotation, if is hard to determine without a variable strobe light.



So,has anyone had this problem or know if this clutch behavior is normal?



Thank you!

- Larry

 

[JCyrbok]

My fan will run at pretty much engine speed when cold until I drive a few hundred yards, 25mph or about 1500rpm, then it disengages. I'm told that this is normal as the viscous fluid actually has to warm up a bit before it will unlock. I know that sounds stupid, but as I drive out of my garage and down the street the you can hear the fan disengage acouple after a couple of houses. The roar of the fan goes away. Try driving a short distance and then checking the fan clutch.



Hope this helps with the trouble shootin'



J-

 

[WestTN]

viscous fan coupling

JCYRBOK is pretty close on this one. The clutch does not need to warm up, but it does need to sling the fluid out of the coupling and into the internal reservior before the fan will 'unlock' and freewheel. Then, the thermal switch will allow the fluid back into the coupling when the sensor sees air at about 205 degrees F coming at it.



Your fan operation sounds pretty much normal. Look elswhere for the cause of the noise.

 

[rparlaman]

fan

i have a 01 and my does the same thing, a few 100 yards and it stops and goes away.

 

[rblomquist]

Just wanted to jump in this thread and see if you guys can help me out with my fan question (or problem). Either my fan is always running or it has never came on. I'm thinking it may be running all the time because there's no way this fan should not be coming on towing an 11k travel trailer in 100-115 degree heat.



When the engine is cold there is quite a bit of resistance when you try to spin the blades by hand, is that a sign of bad or good?



Also, is there anything else you should notice such as when shut down hot i. e. blades freewheeling?



I will add that when running empty I think the truck is running cooler than normal which is making me wonder about the fan being always on. The cummins 180 t-stat I have in there is only about 8-9 months old. Seems to me like the truck should get to 180 pretty easy in this summer heat but the needle stays quite a bit below that until you put a good load on her.





Thanks in advance!