http://www.dieselplace.com/forum/smileys/Ermm.gifWhen pulling my 7400lb trailer with my 2004 DURAMAX/ALLISON in the T/H mode just crtuzin @ 70mph Flat ground or slight hill something cycles about every 4-6 miles sounds like fan comes on slow and winds up then runs for 3-5 miles and then unwinds and quits then just here the engine running, when it kicks on it gets pretty loud.What am I hearing??? 1500miles on the truck..Thanks

It is probably just the clutch fan. I just turn the radio up when that happens.http://www.dieselplace.com/forum/smileys/Big Smile.gif

The fan clutch is tempature sensitive. When the engine is operating at normal or below normal tempature the fan is in slip mode. When the fan clutch sense's a higher than normal tempature it engages the fan and it rev's up, chopping air and making the noise you hear. When the engine cools down and the radiator cools down, cooler air comes thru causing the clutch to dis-engage and putting the fan back into slip mode, no noise. Its normal operation. Edited by: Bill Gisse

You mean that noise that sounds like a jet taking off???Oh the fan kool huh.Least I know its working.Can't even hear after adjusting volume knob on radio...http://www.dieselplace.com/forum/smileys/Cool.gif