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Discussion Starter #1
I am thinking my fan clutch for the past month or so has been starting to partially engage early. Coolant temps have been a couple of degrees cooler and I have noticed it starting to half roar when it should not have to. It has been about 200,000 miles since I have changed it last so it would probably not hurt to change it again.
 

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Mine has randomly done that for years. When it does happen, it's always on a cold startup in the morning.
 

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Discussion Starter #3
The cold morning sickness is normal. This is different after being warm and several hours/miles. For example yesterday when I pulled into a small town it was like 1/2 engaging going down main street. I stop and service a heater then drive 50+ miles to the next town with heavy traffic and it does not engage.
 

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Have you kept a watch on your engine temps when it happens?
 

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Mine never did, but after replacing it last summer when it failed it does pretty much what you're describing. In fact, at time it sounds like its surging in speed off and on as its trying to engage. I've also notice it coming on around town when ambient temps are only in the 80s and my coolant temp is only at around 180. Never did that before.
 

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Discussion Starter #6
It has been very inconsistent so I am just going to replace it. I ordered a new AcDelco one and also a new 145 amp alternator. Since I will already be in there I figured I better have it just in case.
 
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I have the same issue... it's cut my mileage down from 18ish to 16ish. It has the same symptoms... I'll randomly hear the fan start to make noise, then a bit later it will go away.

How's your fuel mileage been doing? The fan adds a lot of drag that you should see in fuel consumption.
 

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Discussion Starter #8
MPG have been all over the place.
 

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Same with mine, all over the place but certainly not better.
 

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Discussion Starter #11
time to make that move to electric 👍
I am kicking myself for not going electric in June when I had the free time. Now is my hell time so until Spring I will be playing heaters.
 
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How do you get the fan clutch out on a Duramax van? I have developed two different ways, and both of them are a PITA.
Start with removing upper fan shroud and use an air chisel on the nut to get the clutch undone. Then either:
1) Remove the grill, undo core support braces and all 8 bolts. That allows to pull the core support a couple of inches forward and get the clearance to get the fan clutch with fan blades out.
2) Get the clutch loose, unbolt the 6 fan bolts, leave the fan blades in the shroud and pull only the clutch.
 

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Discussion Starter #13
The last time I did it I do not remember it being to difficult. The fan shroud is always a PITA to deal with it no matter what.
 
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Discussion Starter #15
Got the fan clutch and alternator changed today. It sure seems to be a lot more quiet than before so I must have gotten used to the noise. Went for a short 20 mile test drive and coolant temps came up to low 190*ish in 75* AAT which is an improvement. Before one day AAT were 90*+ and coolant temps would not go over 186*. Alternator was a little noisy so that was good timing. The extra 40 amps was a nice upgrade.
 

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Discussion Starter #16
I was looking at some stuff on Alldata and GM has a torque spec for the fan clutch that I never noticed before. GM has it at 70 ft lbs which seems excessive. I have never torqued one or even thought about it and have had no issues.
 

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Thanks for the update. Took mine in to the dealership to try and get it fixed or replaced under warranty as they just replaced it last fall. They of course said there were no codes and they couldn't replicate any conditions that I mentioned so there was nothing they could do....
 

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Discussion Starter #18
Thanks for the update. Took mine in to the dealership to try and get it fixed or replaced under warranty as they just replaced it last fall. They of course said there were no codes and they couldn't replicate any conditions that I mentioned so there was nothing they could do....
That sucks and I suppose if it does not happen while driving around the block they call it good.
 

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I think you're exactly right. Seems I'll have to take the tech on a joyride or something and with Covid etc. I'm not even sure what sort of policy they have about that sort of thing. Cluster....
 

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Temps have cooled off into the low 60s here and my coolant temps pretty much never get over 180. Yesterday the fan was roaring as cruised around town with a 175 coolant temp...finally annoyed enough to schedule an appointment and start complaining until its fixed.

Potentially related, any chance an engaged fan clutch would cause a hard start? My van has always fired right up but its actually failed to fire a few time lately and seems like its hard for it to turn over at times. I can always get it to fire on a second go round but something is off. Wondering if drag from the fan if its engaged is making that initial start more difficult?

Batteries are less than a year old and in good shape.
 
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