M1009 Fan clutch question

[n8roro]

How stiff is the fan clutch supposed to be? If spin it by hand when cold it stops almost immediately. Is that normal operation? I could not find any information on this here or online. Thanks for your help.

 

[90Jimmy]

That's how it works, if it spins freely you have no more clutch.

 

[Keith_J]

It requires a few seconds at 700+ RPM to sling the oil out from between the discs before it really freewheels. When it gets warm, the coiled spring on the front opens a bypass valve, allowing the slung oil to drain back between the friction discs, engaging the clutch.

It may roar for a second or two when just starting up, then quiet down

 

[n8roro]

Great, thanks guys. So to verify proper operation, start the engine and wait for the fan speed to slow down.

 

[90Jimmy]

What is making you suspect its not functioning as designed?

 

[n8roro]

I'm was not getting great mileage and have been working through a list of things to hopefully address that. A stuck engaged fan clutch reduces mpg. Also, I replaced the water pump and read that the clutch often gets replaced with that, but I did not do that at the time. In reading about fan clutch operation the stuck disengaged fail is easy to diagnose because the fan spins freely, but a stuck engaged failure seems more subjective. I bought this truck to learn basic mechanics and am learning a lot. This site and the TM's are fantastic teachers.

 

[Sharecropper]

I’ve often wondered how much horsepower is required for a fully engaged fan clutch. I’m certain engine horsepower is lost during full clutch engagement because the “pull” on the engine can be felt when the clutch engages, especially going uphill. I’m toying around with leaving off the entire fan and clutch from my P400 engine build and installing electric fans to free up a few horses. Not sure if the horsepower loss has ever been scientifically measured, but it would be interesting to know that value.

 

[Tinstar]

Remember that when all those electric fans are running, there is more power demand on the alternator, requiring more engine horsepower to turn it.

 

[Matt5]

I’ve often wondered how much horsepower is required for a fully engaged fan clutch. I’m certain engine horsepower is lost during full clutch engagement because the “pull” on the engine can be felt when the clutch engages, especially going uphill. I’m toying around with leaving off the entire fan and clutch from my P400 engine build and installing electric fans to free up a few horses. Not sure if the horsepower loss has ever been scientifically measured, but it would be interesting to know that value.

Uphill... exactly the time it does not matter... you lose HP when cooling is *not* needed as the fan is always spinning somewhat... when you have the electric fans on you would also have the clutch fan engaged... semi sure... electric fans move *less* air than the large clutch fan so... really no reason to put them unless this is a drag racer...

 

[ken]

According to the Hayden website the Severe Duty fan clutch that we use turns at 80 to 90% of the pump shaft speed when engaged. And 20 to 30% when not. So when you turn the engine off, if the fan continues to spin for more that a second or two max it is bad. It should stop almost instantly when the engine it turned off.

 

[Tinstar]

Just installed a new acdelco water pump and Hayden fan clutch on my daughters blazer.
The Hayden fan clutch was made in USA

Electric fans are great, but I will stick to the stock setup for the CUCV.

Good info on the amount of spin provided by Ken.

 

[Sharecropper]

Yeah I think I will stick with my new Derale fan and GM NOS GM clutch. I believe my P400 will have enough horsepower to turn the thing.

 

[ken]

I couple of months back I found a repo of the original 20 inch 7 blade fan used on the civi 6.2 and 454. It's part number OER 3991431. Summit racing is has them for $70. My 82 K20 has this fan. For those of us in hot climates this might be the way to go.

 

[Tinstar]

I couple of months back I found a repo of the original 20 inch 7 blade fan used on the civi 6.2 and 454. It's part number OER 3991431. Summit racing is has them for $70. My 82 K20 has this fan. For those of us in hot climates this might be the way to go.

I will be doing this.

 

[ranger1950]

I couple of months back I found a repo of the original 20 inch 7 blade fan used on the civi 6.2 and 454. It's part number OER 3991431. Summit racing is has them for $70. My 82 K20 has this fan. For those of us in hot climates this might be the way to go.

Would this be a direct replacement for the 5 blade fan on an M1009?

 

[Rutjes]

I bought this Duramax fan blade for my 6.5 K1500. Should fit a 6.2 as well. 4 (m8?) bolts. It's a bit bigger then stock with more airflow. Might require some fan shroud trimming.

 

[ken]

Yes it is a direct replacement. It is the original fan used on the civi models. I installed one on my M1028A1. It works very well.