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  #1  
Old October 1st, 2016, 02:25 PM
JBOD77
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Fan clutch

I've long been curious if my fan clutch is working properly. With fall approaching I have some downtime so here's what I've found. Stock 1995 NAS with 3.9 V8. Engine off the fan can be spun by hand but it stops immediately and has no momentum or free spin. Cold start the fan engages with the start of the engine. Rolled up newspaper applied to fan immediately after starting truck and I can shred the newspaper if I want to. That fan ain't stopping for nothin. Am I correct that this is not how it is supposed to function? Shouldn't I be able to stop the fan upon starting the truck with little to no resistance?
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  #2  
Old October 1st, 2016, 02:44 PM
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Sounds good. If truck is hot and you can stoop the fan with newspaper then it's time to replace.
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Old October 2nd, 2016, 08:27 AM
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So it should run from the time you start the vehicle?? I thought it functioned like a thermostat and engaged when the vehicle was hot and shut off when the vehicle was cool??
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Old October 2nd, 2016, 09:14 AM
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It will always run briefly at start up, then as necessary
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Old October 2nd, 2016, 09:16 AM
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You should be able to stop it when it is not engaged. It needs to get quite hot to turn on and lock up.
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Old October 2nd, 2016, 05:34 PM
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So what I've described is how it is supposed to be? I'm not following
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Old October 2nd, 2016, 05:51 PM
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Thats the way it is. If you want something different, rip out the fan clutch and install an electric unit.
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  #8  
Old October 2nd, 2016, 06:13 PM
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Originally Posted by JBOD77 View Post
So what I've described is how it is supposed to be? I'm not following
No. you should be able to stop it when cold.
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  #9  
Old October 3rd, 2016, 08:20 AM
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So, it sounds like I've got a little project ahead of me..... anyone familiar with a write up on how to do the fan clutch that might be helpful. I've tried searching but can seem to come up with anything....
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  #10  
Old October 3rd, 2016, 10:17 AM
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There is nothing wrong with your fan clutch ... you just haven't tested it when it's supposed to be locked up.

When cold they tend to lock up for a bit ... you here this as more air whoosh from the engine bay.

As the vehicle warms up they unlock and you can stop it with rolled up news paper.

When the vehicle gets really hot they lockup .... this is when the temp gauge starts creeping up well past the middle. They are there to increase the cooling capacity when the engine is HOT

If your temp isn't creeping up it means you cooling system is working well.
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  #11  
Old May 2nd, 2017, 12:22 AM
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reviving an old thread...
I was wondering if the fan clutch gets less efficient as they reach end of life? Meaning... you may not be able to completely stop the fan when it's on, but fan is certainly not as much air as when it was fresh/new?

I ask bc I recently had pretty much all the cooling components replaced (coolant, water pump, t-stat, rodded radiator/flow tested). THe only things that weren't replaced were the hoses and fan clutch.
After driving on the highway at 70mph for about 40min, I hit some traffic at the off-ramp... I noticed the temp gauge started creeping up past the middle. I turned on heater at full and as the traffic inched along, the temp gauge stayed around 3/4 mark (1/4 way before hitting H/red). Once I was moving again, gauge went back to middle.

I had my shop check the fan and they said it's fine (though, I'm not sure how they tested it). When truck is off, there is some resistance if I spin the fan by hand. The fan clutch is likely original (20yo). Trying to figure out if my fan clutch is going and that's why it wasn't able to cool the radiator when I was in traffic?
Thanks!
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  #12  
Old May 2nd, 2017, 03:44 AM
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Quote:
Originally Posted by lithium1330 View Post
reviving an old thread... I was wondering if the fan clutch gets less efficient as they reach end of life? Meaning... you may not be able to completely stop the fan when it's on, but fan is certainly not as much air as when it was fresh/new? I ask bc I recently had pretty much all the cooling components replaced (coolant, water pump, t-stat, rodded radiator/flow tested). THe only things that weren't replaced were the hoses and fan clutch. After driving on the highway at 70mph for about 40min, I hit some traffic at the off-ramp... I noticed the temp gauge started creeping up past the middle. I turned on heater at full and as the traffic inched along, the temp gauge stayed around 3/4 mark (1/4 way before hitting H/red). Once I was moving again, gauge went back to middle. I had my shop check the fan and they said it's fine (though, I'm not sure how they tested it). When truck is off, there is some resistance if I spin the fan by hand. The fan clutch is likely original (20yo). Trying to figure out if my fan clutch is going and that's why it wasn't able to cool the radiator when I was in traffic? Thanks!
Yes these things are flaky. I'd swap out asap and check coolant levels to ensure no air was trapped in system after replaced parts. The fan should roar under warm circumstances. Were you running AC at time? Couldn't of been too hot of a day yet? Start with fan clutch.
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  #13  
Old May 2nd, 2017, 05:47 AM
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Mine is suspect enough for me to have ordered up another. I only put my current one in three or four years ago. The quality of these parts has crumbled in recent years.
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  #14  
Old May 2nd, 2017, 09:39 AM
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Zack was able to get me a nicer quality aftermarket fan last year. Great price. I now need to swap my T-Stat back to genuine since I now run too cool.

It is also handy to have Lav at your disposal to remove a stubborn fan.
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  #15  
Old May 2nd, 2017, 09:41 AM
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Once you figure out how to remove fan, it's a easy swap. I keep an extra on hand expecting one to go out.
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  #16  
Old June 4th, 2017, 06:53 PM
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You keep a spare fan or fan clutch handy?
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  #17  
Old June 4th, 2017, 07:43 PM
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Quote:
Originally Posted by Rocky View Post
You keep a spare fan or fan clutch handy?
Yeah I have 3 Rovers that use the clutch, they don't last as long as they used to.
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  #18  
Old June 4th, 2017, 08:01 PM
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Quote:
Originally Posted by WeBeCinYa View Post
Yeah I have 3 Rovers that use the clutch, they don't last as long as they used to.
Agree on that. Replaced mine today to see if it would improve things. But I think the systems inability to control temp at slow or no speeds might be due to the Water pump. Its getting noisy.

Might be time to ditch that as well.
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  #19  
Old June 4th, 2017, 08:49 PM
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I never run a fan clutch.
Everything about them are a PITA.
An electric fan triggered by a thermo-switch is a much more reliable setup.
With AC you can wire the cooling puller and the AC pusher to both come on when the AC is running.
Likewise the thermo-switch can trigger both fans to cycle on for cooling.
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  #20  
Old June 5th, 2017, 06:48 AM
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Quote:
Originally Posted by lithium1330 View Post
reviving an old thread... I was wondering if the fan clutch gets less efficient as they reach end of life? Meaning... you may not be able to completely stop the fan when it's on, but fan is certainly not as much air as when it was fresh/new? I ask bc I recently had pretty much all the cooling components replaced (coolant, water pump, t-stat, rodded radiator/flow tested). THe only things that weren't replaced were the hoses and fan clutch. After driving on the highway at 70mph for about 40min, I hit some traffic at the off-ramp... I noticed the temp gauge started creeping up past the middle. I turned on heater at full and as the traffic inched along, the temp gauge stayed around 3/4 mark (1/4 way before hitting H/red). Once I was moving again, gauge went back to middle. I had my shop check the fan and they said it's fine (though, I'm not sure how they tested it). When truck is off, there is some resistance if I spin the fan by hand. The fan clutch is likely original (20yo). Trying to figure out if my fan clutch is going and that's why it wasn't able to cool the radiator when I was in traffic? Thanks!
You could also have air in your cooling system. You should also have that double checked. Everyone seems to have different experiences and opinions but over 20 years driving NAS90's as daily drivers I've had to replace one. I personally stay away from electronics on these trucks. They don't ground well IMO and that becomes a ghost chase, whereas a spare fan is easy to pack and trail fix.
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