I've been noticing on cold mornings when I remote start the truck as soon as it cranks and fires theres a "spooling up" sound like the truck is about to take off. I haven't timed it but the only times I have noticed it is when I am loading up the truck, if I start it several minutes before I run out the door I don't hear it. It isn't the same noise Tom reported. My guess is probably a fan, but the turbo isn't out of the question either. If it is a fan, why the heck would it be starting up when things are ice cold?

 

Just speculation, but the cooling fan when the engine is cold could actually help warm it up through higher engine loads. With no fluid going through the radiator no cooling action would be going on, and the extra engine load would require more power which could heat the engine up more.

 

I always said it was the turbo warmup sequence. If it was a fan it would not be that high pitched, and the fan on the 6.7L has an electronically controlled clutch from what I've read. A mechanically clutched fan will rev up with the engine at startup and it's louder.

If the cooling fan was going at turbo-speeds (to create a high frequency close to 10kHz like that) I'd be fearing flying fan blades... these are plastic blades.

 

I have good info for ya. In addition to what Tom says about the fan providing load and making heat, the turbo does spool in a cycle. It will run through some sort of procedure spooling up and down.

I know this because I have the AFE intake which removes the stock air filter box and also the tube, the AFE air tube is just a straight pipe with none of the baffles like the stock intake. Therefore, my engine and turbo are noticeably louder and I can hear the turbo doing all kinds of things much easier than those in stock form.

It's actually pretty neat and I like it a lot. If I think of it I would record the sound but I've never posted a vid or anything like that. Do I have to make a you tube account? Gonna take some time.....

 

The turbo sounds even better with high idle after a cold start.

 

I've been noticing it as well, and I'm putting it down to the turbo spooling up about 2 seconds after the engine starts. Half the time I get a good earful because I'm not in the truck when I start it with the ice scraper in hand.

 

Has anyone heard the aweful turbo sounds a 60 series detroit engine makes when started cold?

 

Hmm... My 6.2 does it as well, the fan seems to ramp up/down at uncalculated intervals when remote started. I bet it's like Tom stated, some type of warm up/startup procedure it's going through...