Load roaring noise/jet engine in my D-Max

[MaxDMax]

I have towed my 12,000lb 5th wheel toybox trailer 4 times with my 2002 3500 D-Max/Allison truck. At times when I am pulling a long steep grade a nosie develops like a HUGE fan is turned on under the hood. This seems to only occur on the longer steeper uphill grades at highway speeds plus. The first time it happened it scared the heck out of me. It is not a ticking or clunking sound, it is almost like a turbine noise of a jet engine. It doesen't happen often, but when it happens it just seems to come out of nowhere. It seems to last through the duration of the mountain when it happens and then slowly goes away after the truck upshifts. All my gauges the trans temp, oil pres.,oil temp, EGT and boost are as expected. Of course on these hills my EGTs are near 1000 to 1100 degrees and my boost is around 22lbs. None of the gagues react along with this noise. I can not say for sure, but possibly it did feel like the engine may loose a slight amount of power during the time period the noise is happening, if so not much. After the 4 outings, it doesen't seem to cause any damage, but does anyone have any idea what/where this super fan noise comes from?

Thanks

[bearman]

It is your engine coolant fan, it is on a clutch, the only time I hear it on mine is when I am pulling hard.
Cheers
Bear

[GreenScape]

I'm here in Fla where it gets hot!!! My duramax does this all the time and so did my 8.1. Both seemed to lose a great deal of power when the fan kicked on. Would an electric fan provide enough air to cool these trucks? I believe it would free up a few HP.

[01_Duramax_Dually]

MaxDMax,
Yep, Big ol Fan clutch engaging to cool motor..Comes on hard then tapers off. I have same thing when towing up steep grades. All is good..No need to worry my fellow 3500 Friend.

Drive it, Let that fan come on..it likes it... :D

[motovet]

I am happy to hear that noise is normal. I heard it last weekend for the first time while pulling my trailer and all the race stuff. Really freaked me out,and probably the guy next to me I was sharing a lane with at that moment.

[mps007]

First time i heard a noise like that was when pullin 78k up a hill with a 400 cummins in a Freightshaker.........

I love that sound in my Dmax ------- raw Power !!

[MaxDMax]

Thanks for the info, I feel better now! I guess since I bought my truck in the middle of the winter it has not really needed the cooling fan more than 4 or 5 times at 6,000 miles (cool). I kind of hoped this was what this was, but this is NOT your average extra cooling fan. By the sound of it you would think the truck would speed up due to the increased airflow! This goes to show you that this thing is built to do a LOT MORE than I have actually thrown at it. Guess I will hear it more often this summer. I don't know about you all that are pulling 12K or more, but the truck I had before this was 2001 Z71 w/5.3 SB Ext. cab and thought I had a truck then, no way! I really love this truck and drive it every day and will be taking my Son Motocross racing almost every weekend this summer and fall. I have already decided to extend out ventures by 200 extra miles whenever possible just so he can get his hands on better competition AND (I get to drive my D-Max more!). So now I got to put this into prospective:
a. I had a GMC 4.3 4 door GMC Jimmy and my 3K box trailer made me nervous stopping and the thing was slow on the hills.
b. I get a 5.3 Z71 and thought things were great. Pulls nice, but at times got bogged down to 50mph on the bigger hills.
c. I get a D-Max and I pull my little 3k box trailer and it seems like it is not even there.
d. I get a 36.5 5th wheel foot toybox trailer, and run it as light as possible no water just the basics and it pulls easier, faster and safer than my Z71 pulled my 3k box trailer.
e. I decided to give it a shot with the whole Family and believe me my wife packed everything, 3 race bikes, everything we could load in the trailer, generator, air compressor, 110 gallons (900 plus pounds) of fresh water, a 500lb tool box, 2 TVs, extra race gas, generator gas and all the food we could carry. And the trailer pulled great, felt even more stable, the truck road better and I could not tell I added a pound. I caught my self driving 75 and 80 mph at times, no intentionally mind you it just kept feeling like the sweet spot for the hills and the engine.
I guess I will go weigh the thing this week to see where I am on weights and see just how much more I can take with me! I definately don't want to overload my trailer pased it's gross weight of 13,500lbs now do I. Got to love this truck!

Thanks Again,

[ 04-10-2002: Message edited by: MaxDMax ]</p>

[DeanysDiesel]

Boy was I glad to find this discussion. I was towing my trailer out to west Texas at the end of March and I heard the same "jet engine sound". I thought I blew something and pulled over but all was well. This was the first time that I pulled my trailer with fairly warm air temperature.

I will say that it was pulling great :D and I was just enjoying the power :D :D . Now I know hat the sound is and it is just another part of the truck that is ding its thing. Boy do I love this truck. smile.gif smile.gif

[mcfly]

I will hear the same noise but under different conditions. Sometimes in the morning when the motor is not fully warmed up, I will hear the same sound described by MadMax. It usally only lasts for a few hundred feet then goes away. I figured it was the fan engaging. Should it be engaging when the motor is cold? Do I have a problem that should be addressed at the dealer?


-Rick

BTW My mileage has increased slightly over the last few tanks to 16.5 mpg. The only things I have done were tow a big boat about 100 miles. Up the tire pressure to 65psi in front, 65psi in outside rear and 60psi in the inside rear.

[More Power]

You can read more about fan-clutch operation here:

http://www.thedieselpage.com/reviews/fanclutch.htm

This story is primarily about the 6.5, but it also contains some info about the Duramax.

MP

[ 04-10-2002: Message edited by: More Power ]</p>