We are in the process of towing our 12000# fifth wheel home from Arizona. While in Arizona I reprogrammed for 50 more horsepower using the Hypertech. I noticed while hauling thru rolling hills of Tenn. a noise I had not heard before. Once in a while while towing in overdrive I hear a noise that sounds like I have down shifted, but the rpm's don't change. This has happened both going uphill and down. The noise lasts for a minute or so and ramps down to normal. I returned to stock factory settings and have not heard it since. I do remeber, however, hearing the same thing on the way to Az. This happens very infrequently - what am I hearing and is it something to worry about. By the way when I returned to stock settings I had no DTC's.

Could it be your clutch fan kicking in? Is your temp lower after the noise stops?

I have heard the same thing with mine. Sounds like the tranny is really winding up but the rpm's don't change, nor does the tranny temp change. Can last for several miles before it slowly goes away. Mostly happens while towing but I have noticed it a few times in the morning when starting cold. Will last a mile or two then goes away.

Mike

Both mine do the same thing.Like Dmaxcan said its the fan clutch.At least mine is.

I agree, I hear my fan clutch once in a while.

Waste gate?????????????????????


Geno

Fan clutch for sure.


Its normal and right.


Blake

Talk about timely. I guess I am ahead because I figured it was the fan clutch. I am towing about 8k lbs and running 70 mph. The outside temp was showing 88 deg. While the engine showed a constant 205 deg and the trannie showed a constant 180 deg. Dang that thing is loud.http://www.dieselplace.com/forum/smileys/Angry.gif I can not belive the fan was necessary running 70 mph. http://dieselplace.com/forum/smileys/Confused.gif So you think this is normal? If it is I am going to have to go to an electric fan to keep the temps down so I don't have to listen to that noise when towing.

I think the fan clutch is a shocker first time you here it for every one!! question? what is DTCsEdited by: mongo

Digital trouble codes

We are in the process of towing our 12000# fifth wheel home from Arizona. While in Arizona I reprogrammed for 50 more horsepower using the Hypertech. I noticed while hauling thru rolling hills of Tenn. a noise I had not heard before. Once in a while while towing in overdrive I hear a noise that sounds like I have down shifted, but the rpm's don't change. This has happened both going uphill and down. The noise lasts for a minute or so and ramps down to normal. I returned to stock factory settings and have not heard it since. I do remeber, however, hearing the same thing on the way to Az. This happens very infrequently - what am I hearing and is it something to worry about. By the way when I returned to stock settings I had no DTC's.

I had this same experience. Asked the question, looking for what caused it on the 2300HD thread. Got multiple answers. I don't believe it is fan clutch but to each their own. There was one answer that sounded like a good technical answer... an aux fan that kicks on, thought to be initiated by intercooler temps. It is said to be quite normal and if the correct answer is the aux fan for intercooler temps it seems valid and normal when towing, particularly if towing up and down grades.
Maybe we can get one of the tech's to chime in to verify an accurate answer.

Sparkyp Edited by: sparkyp

I don't believe that there are any "auxillary" fans on our engines. The fan on our truck comes on all of the time when pulling our trailer (about 10k lbs loded) even when the outside temps are cool, especially when going up a steep or long grade. I wish the fan was electric instead of engine driven to cut down on noise and power loss.

It is the fan kicking on cooling the temps down...this is normal when working the truck and it will do it no matter what the outside temps are, though it will do it more so when hotter out...if the engine gets warm while working hard it has to cool down...just like a human has to cool down when getting over heated. Its just a characteristic of a diesel engine and it doesn't bother me to hear it or any other diesel engine noise. Those sounds are sounds of a hard working truck doing its job and boy do I love the sound of that!! Wouldn't trade the sound of a diesel for nothing, No. 2 diesel fuel flows through my blood I think,...I was sad & angry when they made them quieter. http://www.dieselplace.com/forum/smileys/Angry.gif


If you think the noises that your Duramax makes is loud you should sit behind a 550hp Cat or Cummins Diesel in a Pete379 big truck for thousands of miles....http://www.dieselplace.com/forum/smileys/Heart.gif


Edited by: GMC Cowboy Cadilliac

The fan clutch is activated by the heat flowing out of the radiator. It is possible that your clutch is activating too soon. Take it to the dealer, they have a procedure to test the proper operation.

Yep, I vote fan clutch. I heard it the first time pulling my 6k TT up toward Fancy Gap VA on I-77. Thought it was not good until I remembered what I read here. You have to really load the pig to get her to squeal. I had the cruise set for 70 and only backed down from fear. I-77 is not real Truck and Trailer friendly. http://www.dieselplace.com/forum/smileys/Big Smile.gif

It's the fan. I've had mine on for 100 miles straight in 105 degree heat pulling a gooseneck with a 15000lbs forklift on it. if you work it, you got to cool it.


If you don't like the sound of it buy yourself a little bitty Toyota. Maybe you won't hear it.

I am all for cooling a hard working engine and I believe I am working it a little pulling 8k lbs but I am running 70 mph. How much more cooling can that fan provide at that speed?