Viscous Fan Clutch - how stiff is yours?

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firemanshort
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Viscous Fan Clutch - how stiff is yours?

Post by firemanshort »

I think my viscous fan clutch it worn out. I think it may be "loose" or in the "cool temperature mode" all the time - but I have nothing to compare it to so I do not know.

When my truck is cool - I can reach in and turn the fan blades with the motor off. The fan will turn - but it does not free spin like a roulette wheel. It just moves when I push it and stops when I let go.

When the motor is hot - I get the same experience when the motor is off.

What I do not know is if it takes the spinning motion to get the viscous part to lock up or not.

My symptons are that the truck starts to get hot when I am sitting still for a long time. If I stop at an off road event in a line of cars stopped at an obstacle then the temp will slowly creep up. If I crawl around at 2 - 3 MPH then I get the same thing. As soon as I start to move and get some air flowing accros the radiator, the temp needle starts to drop down back to the normal level.

Can someone share thier hot motor / turning the viscous fan by hand experience?
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noexitroad
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Re: Viscous Fan Clutch - how stiff is yours?

Post by noexitroad »

good question there mate. the manual describes it as an "inertia damper" which sounds different to a viscous fan.
somebody else will need to step up to answer this one :?:
disco2hse
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Re: Viscous Fan Clutch - how stiff is yours?

Post by disco2hse »

I would first check that you have a full head of coolant. That is, that you haven't got an air block in the top of the motor. Also, when was the last time you did an engine flush and had the radiator rodded?

The symptoms you describe relate more to those issues or low coolant. Similarly, have you checked your oil level and quality lately? When was the last time you did an oil and filter change or did an engine oil flush? Blocked galleries or a blown head gasket can cause the symptoms too.

If it is none of those, then it may be the viscous fan. They are cheap enough to warrant fitting a new one. It's just getting the damn thing off that's the problem.

I am not a fan (no pun intended) of electric fans unless you are doing something really different, like fitting a bigger block or moving the radiator to the back.
Alan

1983 ex-army FFR 109 Stage 1
2005 Disco 2 HSE TD5
Glen
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Re: Viscous Fan Clutch - how stiff is yours?

Post by Glen »

I think they do need to be spinning to get a really meaningfull load from them. They also don't usally go fully locked or fully unlocked, but vary between say 80...20% slip.

I noticed on my mates stage 1 its got quite a roar to it even when cold and you can feal it pulling a lot of air through the grille on idle - I wonder if thats a bit keen.

I have a Range Rover 300Tdi and while its windy under the bonnet when the engines running, the grille doesn't feel exsessively drafty (not say like an electric fan would do) and it doesn't normally roar (I don't rev it instantly after starting and its an automatic so tends to get a good bit of idleing to ster it up before I rev it. I have however noticed if the weather is warm (for the UK) and especally if I've already driven it in the last couple of hours it does roar in 1st and 2nd gear when pulling away but then goes quiet again - I put this down to underbonnet tempreature and the hot engine being enough to make it lockup but once you get moving it pulls enough air to cool back down - I think that feals about right though as with all viscous couplings, you never quite know unless its a brand new one (its a question more often asked by people with Viscous coupled 4WD like some Range Rovers, Freelanders and Volkswagen Transporter Syncros as they get expencive when they go stiff).

Never roars - gone slack
Only roars after starting especally when hot or when stuck in traffic - about fine
Roars all the time - Gone stiff

When working properly these things will piss all over an electric fan though, think they can take over 3 kW off the engine when locked up which is gonna take one hell of an electric motor to match - One of those Kenlowe fans is okay for a toy car in the UK but if you tow with it or go to hot places I wouldn't fit one to a diesel (been there, overheated) so it'd be a very bad idea on a V8.
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firemanshort
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Re: Viscous Fan Clutch - how stiff is yours?

Post by firemanshort »

I am not so sure about my original diagnosis, now. I have spent a lot of time looking at the fan and it looks like it is spinning fast on idle and I can place my hand in front of the radiator and feel a little air pull at idle - so I think the fan is fanning.

I may have another undiagnosed cooling problem.

I am also bearing in mind that this occurs when the temperatures are well above 90 degrees F. I took a trip this past weekend and got a slight temp increase when I was climbing a long slow rock strewn hill (maybe a mile climb in 2nd gear / low xfer) - but as soon as I crested the peak and started downhill, the tempereature dropped like a stone.

(Maybe this is just normal and I am worried about nothing...)
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disco2hse
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Re: Viscous Fan Clutch - how stiff is yours?

Post by disco2hse »

Refer to my previous post. It is not normal for the temperature to rise and fall quickly. Some degree of variation is normal, but it should not be quick.

Again, what you describe are issues to do with lack of coolant. When was the last time you had your radiator rodded, engine flushed, etc?

Have you checked for a blown head gasket?
Alan

1983 ex-army FFR 109 Stage 1
2005 Disco 2 HSE TD5
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firemanshort
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Re: Viscous Fan Clutch - how stiff is yours?

Post by firemanshort »

My radiator was re-cored a few years ago (maybe 2009). The old core was completely blocked with sediment and it was leaking in a few places. All that is left of the original radiator is the side tanks.

My engine was completely rebuilt in 2011 - so it had better not be the head gaskets. :evil: It is not using / losing water either.

Maybe I have an air bubble in the system?

More looking is definately needed.
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disco2hse
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Re: Viscous Fan Clutch - how stiff is yours?

Post by disco2hse »

Also, check the heater matrix is not blocked.

You can have a blown head gasket and not have water in the oil or be losing water.
Alan

1983 ex-army FFR 109 Stage 1
2005 Disco 2 HSE TD5
Mrs Bingham
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Re: Viscous Fan Clutch - how stiff is yours?

Post by Mrs Bingham »

For what it is worth the action of your viscous coupling sounds exactly the same as mine and I have no cooling issues at all even when towing, although I appreciate that in Blighty we don’t drive around in 90 degree temperatures :D

I thought my fan was too stiff say compared to cars I’ve owned in the past, but as I’ve mentioned above I don’t have any cooling issues and I don’t get any fan roar. At idle the air flow through the grille will easily hold a piece of A4 sized cardboard hard against it.

My thinking is drain the coolant out and flush it out thoroughly and note how much it takes to refill and compare that figure to the manual. Are all your hose temperatures even when at full running temperature? Is the thermostat the correct one for your environment and is it operating properly? Do a block test (the blue fluid test) to rule out a head gasket. If you are not actually overheating it could simply be a dodgy gauge or sender unit!
1983 Stage 1 V8 Hardtop (Mrs Bingham)
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