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When I start out with a cold engine I let it warm up for a few minutes at idle and then drive it easy until the temp comes up. What I have noticed is until the engine temp gets above 165 or 170 the engine has a real growl to it. Sounds like the engine cooling fan is being blocked or somewhat like the sound of aggressive off road tires when on a paved surface. As the temp rises the sound disappears. Any ideas on what I am hearing?
 

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I tried to describe the same noise and was told it's the "Allison Whine". It may be your tranny and if it is it's perfectly normal; so I've been told.


Truck on!!!:cool:
 

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I think its the cooling fan. Mine comes on for about the first couple miles i drive a day. It usually goes off once at about 35-40mph though.
Thats the only time my fan kicks on.
 

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It's growling because it's hungry, now go feed it a Dodge or Ford. Once it gets it's belly is full, it shouldn't growl any more.
 

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Mine does the same thing, and it is more promenant the colder the outside temperature is.
 

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Yea mine does it also, but at all speeds and temps. You can feel it just a small bit throught the floor boards. But only if there is a load on the trans. If you go to idle while rolling at speed its gone.
 

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Mine does the same thing. It sounds like the cooling fan comes on when it's real cold out, although I cannot see why the fan should be coming on when the engine is cold. It could be that the silicone fluid in the fan clutch is too thick when cold. I dunno!!! :confused:
 

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Mine does it too. Same sound as when it's really hot. From everything I know it is the fan. My guess is either the fluid like someone else mentioned or it is engaged to put extra load on the engine to warm it up.

I know I don't live in as cold of weather as most of you but I just let mine warm up a little more before driving.
 

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who else wishes they could have a manual switch for that fan?

That deep loud sound even turns trucker's heads:ro)
 

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The fan clutch should be disengaged when its cold. Mine makes extra "fan" noise but it goes away after it warms up alittle. If I let it warm up first before driving, I don't get the noise at all. I notice quite different (less) power too.
I think its the turbo and not the fan. When cold, the turbo will restrict the exhaust to help warm up faster, sure sounds and feels like what's going on.
 

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The fan clutch should be disengaged when its cold. Mine makes extra "fan" noise but it goes away after it warms up alittle. If I let it warm up first before driving, I don't get the noise at all. I notice quite different (less) power too.
I think its the turbo and not the fan. When cold, the turbo will restrict the exhaust to help warm up faster, sure sounds and feels like what's going on.
Makes sense.
 

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I thinks its just the cold silicone in the fan clutch causing the fan to engage. It has a high sheer force and needs a little friction to warm it up and allow the fan to slip. If you pick up a little speed 20 to 30 mph then then take your foot off the accelerator allowing the air to push on the fan it usually helps the clutch disengage.

Take a look at this link for a little info on how a fluid fan clutch works
http://www.innerauto.com/Automotive_Systems/Cooling_System/Fan_Clutch/
 

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I believe the owner's manual (or Duramax engine manual?) says you may hear the fan at initial start/warm up and it is normal.
 
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