Mechanical engine fan in '05 Durango vs '05 Grand Cherokee

The mechanical engine fan is very noisy on startup in my '05 Durango 4.7L -- sounds like a hurricane on startup and takes a minute to quiet down. I
realize this is normal and why it happens.
But the mechanical engine fan in my '05 Grand Cherokee 4.7L is very quiet on startup! Does anyone know why? I believe the Durango 4.7L uses an ordinary viscous drive with no electric connection -- perhaps the Jeep may have an electrically operated clutch of some kind?
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You may want to post this in the truck section, I dont work on Jeeps/Trucks but im pretty sure that the fan on the Jeep operates off hydraulics from the P/S pump and not a mechanical fan
Glenn Beasley Chrysler Tech
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Marcus wrote:

On my 2004 Hemi Durango the fan on startup or normal driving is very quiet. When the engine gets a bit hot such as when I tow up hill in the summer the auxiliary fan turns on and it is VERY loud.
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On your Hemi, don't you think the loudness is the clutch engaging, making the primary engine fan become loud?
On my Durango 4.7L, the fan is quiet as well normally. It's just on startup that I hear the hurricane for about the first minute of operation, or I may hear it for a few seconds if I've been sitting at a red light for a minute -- the heat builds up a bit making the clutch engage.
In the past I've read that on the ordinary viscous coupling the silicone fluid has to work its way out of the clutch grooves so that the fan can spin more slowly. From that point on, only heat should cause the viscous coupling to engage, making the fan louder -- such as when towing.
It's no big deal, of course. But that Jeep 4.7L sure is nice and quiet on startup, so it got me wondering. Got me thinking maybe I it's just a different clutch design and I might switch it. ;) Most likely there's some complication that makes a swap impractical or impossible anyway.
Marcus

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I have 2 older Dakotas (98 and 00) and when they are cold the fan will do that. It also does it when the engines get to a higher temperature to where the clutch on the fan engages and the fan spins faster. That is normal and by design. It's when the fan makes squealing, grinding, or other "non-wind" related noises or stops turning altogether, is when you need to start being concerned. The clutch fan is just that - it has a sealed hydraulic clutch that engages when engine temperature gets high enough for it to engage. You can turn your fan blade by hand whith the engine off. There should be resistance to it. If there is none you may want to get it checked out.

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Thanks, but the question was why my '05 Grand Cherokee 4.7L does not make that startup hurricane noise. The Jeep's 4.7L is quiet on startup while the Dodge 4.7L has the hurricane noise. I would assume the two 4.7L engines would be basically identical, especially for something as mundane as the fan coupling.
I have the manual for the Dodge and it uses a standard viscous coupling, but I don't have a manual for the Jeep yet. I thought perhaps someone here might know how the Jeep 4.7L runs its mechanical fan, assuming it doesn't use an ordinary viscous coupling like the Durango uses.

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Marcus wrote:

Dunno. All I know is that when the engine starts to get warm I hear a VERY loud roar and the temp quickly comes down and the roar stops.
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