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Discussion Starter · #1 ·
Wondering if anyone else has heard this. Most noticeable on hot days after work for the first few miles the engine sounds very loud. Sounds like the motor is revving much more than it actually is and is most noticeable around 1750 - 2000 rpm. After a while it quietens down. I almost never hear it first thing in the morning or on cooler days. The difference in engine noise at the same rpm is pretty big.

Any ideas?
 

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Discussion Starter · #4 ·
I think what you're hearing is the radiator fan kicking on and off. My Ram 2500 CTD would do this as well.
No I wouldn't think it is the radiator fan. Only happens for the first few miles on hot days after a 'cold' start.

I don't know nearly enough but my first thought was turbo oil or something with the variable vanes but it is not a wining turbo sound so that confused me. It sounds like the motor is free revving to about 4000 rpm but it is actually only around 2000. It is rpm sensitive, I don't hear anything below about 1500. After a few miles I purposely get the rpm back in the 1750 - 2000 range and it no longer is noisy.
 

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It's the rad fan. They are huge in this truck. Even on a cold start on a hot day. Odd are you have your a/c on which also will trigger the rad fan especially shortly after start. Once the truck senses it doesn't need it it will die off (maybe 3-5 min). Because our fans are mechanical it will be rpm sensitive too

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I think redbolt nailed it. I have more noise on startup on a hot day for the first few minutes, rad and a/c fans?
 

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Discussion Starter · #8 ·
Thanks all, makes perfect sense. For some reason I thought we had electric fans. Bought the truck last September and didn't start hearing it until June. That's when we started getting some ambient temps in the 90's which is only when I hear it.
 

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Colorados have electric controlled clutch on engine fan. Not electric fan. Mine does same, it's normal I assume. When warm and ac on to start cooking the condenser. It quiets down once get some road speed


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As noted, it's definitely the fan. I hate it.

I have the electric fan parts from a V6 on hand to do the conversion but haven't tackled it yet. The V6 assembly drops right on to the radiator with the same tabs and all, I'll have to run power and ground and one wire from the ECM from what I can tell, and then just some tune changes.
 

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I love the clutch fan! I think it's a brilliant compromise between reliable driven fan and simple control. Or precise control. I don't know if it will stay reliable though lol


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They aren't reliable, that's the problem. They've been unreliable on previous models and quite a few people with our diesel have already had problems.

They have this fan because a manual fan moves more air than an electric fan and GM makes sure to put a manual fan on anything that's intended to tow to help avoid cooling issues.

It impacts power and mileage though, although not any more than the air dam I'm sure.

I hate the noise. I feel like I'm back in an 89 Suburban every hot day that I drive it.
 

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Watch that whining sound closely as that's how my two clutch fan failures started. (yes two -- see my post today) The noise gets worse and pretty soon you will see the temp gauge climb, eventually getting the "overheating" message. This stranded me this last weekend on a busy interstate. This particular clutch fan design appears to be a pretty crappy one.
 
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