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wxmn6
10-10-2002, 13:47
Today was my first day pulling a trailer. The trailer is 6'7" by 12' landscape. When I was driving on interstate this morning, about 30 minutes after I left my house, I heard something that is sounding on and off. I am not sure what it is but it sounds high pitched, something like whistle or air hissing. The sound would come on and last sometime for 2 seconds, sometime 5, 10, 30 seconds before it would stop and start again. My truck have Jordan brake controller and I was going 65 MPH when it the sound started somewhere in my truck. All my gauges looks fine, no message coming up on the dash at all. Transmission temperature was at 150, water temperature was at 190. It did the same thing when I went back home this afternnon. I thought that it might be because 65 MPH is too fast, but the sound continue when I am doing 40 MPH on small road. It is the first time that I heard anything like this. Any idea what it could be?
dcpdave
10-10-2002, 23:51
wxmn6,
if this noise only does it when the engine is warm, try to pay attention to what the rpm's are when it comes in. if it comes in around 2200-2500 rpm's, then it's possible that it is coming from a restrictor in the heater hose. g.m. put this restrictor in to prevent a "gurgling" noise as the coolant goes thru the heater core. the noise should be audible even sitting still, and in that rpm range. if this is it, g.m. is recommending removing the restrictor. we have done this to a few vehicles and it has fixed it. i was kind of afraid that by doing this, we might re-introduce the gurgling noise, but it hasn't yet.
hope this helps,
wxmn6
10-11-2002, 11:33
Never heard about it. Thanks for the information. Today I went the same way I went yesterday but without a trailer and I never heard any unusual sound today. I think the RPM was at around 2200-2300 when pulling trailer yesterday, but today the RPM was at around 2000-2200 (without trailer).

Exactly what kind of noise do the restrictor sound like? Is it harmful or bad for my truck if I continue to use it when it is making noise? Thanks.
dcpdave
10-11-2002, 11:58
wxmn6,
the noise sounds like a somewhat higher pitch air noise, a "hoot" type. if you feather the throttle you should get it to come and go. it sounds like it's coming from the center of the dash area. it will not hurt anything to keep the restrictor in the hose, it's just annoying sometimes. it has only been present on gasoline engines;5.3L,6.0L, and 8.1L .
hope this helps,
wxmn6
10-11-2002, 13:31
Yeah that's exactly what I heard yesterday. I uses my trailer for transporting my lawn care equipment at a short distance almost all the time so I think I won't bother doing anything with the resistor. The reason I brought the trailer on a long trip yesterday was because I have to bring the supplies from a store. Thanks for your help! smile.gif
Hoss
10-15-2002, 14:35
dcpdave,
i too have a high pitched whine.... sounds like a hyd pump going bad. It comes and goes as I feather the throttle, but I notice it at around 1500-1900. Could the restrictor be causing this as well? Where is the restrictor located, upper or lower hose, and at which end? This noise is irritating as hell, and the dealer can't seem to find it. I will fix it myself once I know where the restrictor is. TIA.
hoot
10-15-2002, 16:32
Hoss,

The Allison makes that whining hydraulic pump noise because it has a hydraulic pump and it's not what you are used to hearing from a little car automatic.

When it starts getting colder out, it gets louder. Mine is very noticeable now. In the summer you hardly hear it.
dcpdave
10-15-2002, 20:44
hoss,
the restrictor is located in the heater hose where it attaches to the bypass tube at the water pump, but that is ONLY on the 5.3L, 6.0L, and 8.1L gas engines. the duramax has a different design and there is no restrictor.
i would be inclined to think that hoot might be on the right track with the allison pump noise. the allison is a heavy duty transmission, and therefore, has a high volume-heavy duty pump in it, and yes, it is noisy.
wxmn6,
to verify the restrictor as the noise in your 6.0L engine,take a pair of plyers and have someone pinch off the heater hose that goes to the water pump while you are sitting in the truck duplicating the noise and see if it goes away.
hope this helps,
Hoss
10-16-2002, 18:31
Hoot,
This is not a constant noise... it comes and goes. I have ridden in 2 other trucks and neither of them made the same noise. I pull a 13k trailer almost daily.... and it makes the noise with and without the trailer.... Any suggestions as where to look??
hoot
10-16-2002, 19:15
Mine also comes and goes as I feather the throttle. Especially in the morning when it's cooler out.

It's hard to tell if you and I are talking about the same sound without actually hearing it. Mine is a hyd pump sound that changes pitch with engine speed. That's what the tranny pump does. Some Ally's are louder than others.

I know they made some changes in that pump for the 2002 model year to make it a bit quieter. I don't mind it.
Hoss
10-22-2002, 15:00
mine doesn't change pitch with throttle.... always the same pitch. I need to fing the source quickly.... 30k on truck now and want it fixed before warranty expires....
hoot
10-22-2002, 17:18
Just make sure they know and it's documented. Even if they can't fix it during warranty, they still usually honor the warranty for a pre-existing problem that started during the warranty period. At least that's been my experience.