4.0 Viscous Fan

RBBailey

NAS-ROW Addict
Callsign: KF7KFZ
I'm used to the viscous fan on the Rover V8 being "on" for the first 30 seconds or so of a drive, then I'm pretty sure they are mostly free spinning unless the temps get up, and then it engages.

However, yesterday I noticed that my fan was always engaged. It was a cold start, and like normal, it didn't get to normal temps till 3-4 miles down the road. But the fan was engaged the whole 10 mile drive. And when I opened the hood to just double check, it was easy to tell that the fan was engaged, not spinning freely with the engine off.

Any thoughts? I don't know, but I hadn't ever thought about the possibility that it might break and stay on. I always figured a broken fan would never engage.
 

The Dro

Illustrious
That's typically the normal issue when the valve doesn't open. It won't allow the silicon viscous fluid to circulate through the plates to "engage" the fan.

How cold was it outside? The only thing I can think of is that the silicone was not flowing properly because of the cold. This silicone is like the consistency of honey.
 

RBBailey

NAS-ROW Addict
Callsign: KF7KFZ
Interesting. For some reason I was thinking it was some kind of heat activated spring.

It was about 45 degrees.
 

pmatusov

Technical Excellence Contributor
Callsign: AK6PM
I don't know, but I hadn't ever thought about the possibility that it might break and stay on. I always figured a broken fan would never engage.
I had two fan clutches that froze solid. It is usually not good news for the fan blades.
 

RBBailey

NAS-ROW Addict
Callsign: KF7KFZ
Was wondering what consequences there might be. Thanks.

I drove it tonight. Fan was stuck for 6 miles. Then on restart after sitting for just a few minutes, the fan was stuck on, but seemed to start coming loose, then went completely back to normal. On the third drive, it acted normal all the way through.
 

The Dro

Illustrious
Interesting. For some reason I was thinking it was some kind of heat activated spring.

It was about 45 degrees.
There are spring engaged fan clutch out there... but not the Rover.

The coil you see in the from it's a bi-metalic coil that expand/contract with the temperature changes to open/close the valve so the viscous fluid exit the reservoir.

That's cold... I'd be worried if the fan doesn't spin when is warm.
 

The Dro

Illustrious
Was wondering what consequences there might be. Thanks.

I drove it tonight. Fan was stuck for 6 miles. Then on restart after sitting for just a few minutes, the fan was stuck on, but seemed to start coming loose, then went completely back to normal. On the third drive, it acted normal all the way through.
I think it's because of the cold weather
 

DiscoDavis

Well-known member
I have a bearmach one, it stays locked on when cold for a few minutes then unlocks after driving a bit. Old one was just locked on all the time, jet fighter status
 

The Dro

Illustrious
If you are concerned about the fan clutch you can easily replace it with any of these:

Hayden 2626 Light/Medium Duty
Imperial 215157 (I think now it's carquest) or Hayden 2786 Heavy Duty
Imperial 215158 Sever Duty... But I don't recommend it, unless you are doing heavy wheeling or want permanent hearing loss.

Get the correct bolts.... Dorman 14040

I've used both LD and HD ones and they did the trick... and cheap.
 

RBBailey

NAS-ROW Addict
Callsign: KF7KFZ
I drove it yesterday, and this morning, and it acted normal for both of those drives. On for a minute or two, then it releases. Seems normal. But probably something I'll have to show my kid how to replace at some point. Thanks for the part numbers.
 

mitherial

Well-known member
Basic question about the viscous fan (on the 19J engine in my case): how tight should the center nut on the fan clutch be? Specifically, should the plastic fan blades spin at all without engaging the pulley-rod? I can't remember how mine was before I started tinkering with it, and now it is starting to get warm enough for engine cooling to really matter.

The workshop manual lists the "Fan Assembly to Water Pump Hub" as 16-20 ft.-pounds, but I assume those are the four bolts in the second picture, not the single bolt keeping the plastic blades from flying off.
 

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mitherial

Well-known member
I understand how the viscous clutch will engage/disengage as a function of temperature, but for that to work does the center nut need to be tightened to attach the movement of the blades to the rotation of the clutch itself?
 

Jeff B

Well-known member
Basic question about the viscous fan (on the 19J engine in my case): how tight should the center nut on the fan clutch be? Specifically, should the plastic fan blades spin at all without engaging the pulley-rod? .

I've always just barely snugged them because the rotation keeps them tight.
I also put a little smear of silver anti-seize in the nut because these are always hard to remove...


.
 

The Dro

Illustrious
I've hand tighten my... :eek: NEVER had a fan issue in any of my Rovers. ;)


They spin the same rotation as tightening it.
 

rlynch356

Well-known member
yep don’t over do it and use anti seaze.. that said if you have on the this stuck ON.. when you replace it, throw that one in the trail spares box... b/c its better to be stick on than off.. and its a free spare so to speak.. had them break in the OFF poisition which sucks for getting you home when its hot.. and carrry both the fan wrench and the holder tool.. the Nut comes off to the drivers side (down) btw...
 
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