Test Fan Viscous Coupling

Hi
Could someone please tell me the best way to check the fans viscous coupling on a Classic RR 3.5.
Thanks

rolled up copy of LRO International or Readers Wives..if it stops the fan spinning its fooked

+ 1 for the rolled up paper/mag.
Better still use the Sun, all that's any good for
If it's a 3.5efi it should have an 11 blade fan, carb versions were 7 I believe.

Thanks for your responses, should I wait until the engine is hot before testing?

dougc said:

Thanks for your responses, should I wait until the engine is hot before testing?

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If it is like the P38 it will be locked on startup, loosen up and go quiet as it warms and then tighten up again when hot to stop overheat.

If loose all the time and can be stopped with a newspaper it is stuffed. If solid all the time and shreds the paper then it is stuffed.

dougc said:

Thanks for your responses, should I wait until the engine is hot before testing?

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Yes

With the engine cold, start and rev it once, let idle for a minute or so then stop it. The fan should then be turnable by hand. It should free up further the more it is turned. If it is stiff to turn and cannot be stopped with your finger tips at cold idle it is on it's way out. DO NOT try the finger tip test if you don't know what you are doing.

he didn't know what he was doing!!!

Mark Piercy said:

View attachment 187930 he didn't know what he was doing!!!

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Obviously not a time served mechanic of more than fifty years standing. Who still has all his fingers.

wammers said:

With the engine cold, start and rev it once, let idle for a minute or so then stop it. The fan should then be turnable by hand. It should free up further the more it is turned. If it is stiff to turn and cannot be stopped with your finger tips at cold idle it is on it's way out. DO NOT try the finger tip test if you don't know what you are doing.

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^^^^This.
That's what LRO or Readers Wives/The Sun are for.

Thanks everyone for the information. With the engine hot should it be impossible to stop the fan with a newspaper or just require a great deal of pressure?

dougc said:

Thanks everyone for the information. The viscous drive did not pass the newspaper test which results in another question: Is it possible to remove the viscous drive without having to remove the fan (I have an 11 blade fan).

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Not as far as I'm aware, the fan is bolted/riveted to the viscous coupling. You could always bin it and fit an electric fan.

Datatek said:

Not as far as I'm aware, the fan is bolted/riveted to the viscous coupling. You could always bin it and fit an electric fan.

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It is a complete unit as you say. Some fit the fan from a 300 Tdi which does have a separate fan and viscous unit.

Thanks. It is a separate unit, with bolts through the rear of the fan. I was just wondering if it could be removed by just removing these bolts.

If the viscous drive is working correctly should it be impossible to stop the fan with a newspaper or just require a great deal of pressure?

dougc said:

Thanks. It is a separate unit, with bolts through the rear of the fan. I was just wondering if it could be removed by just removing these bolts.

With the engine hot should it be impossible to stop the fan with a newspaper or just require a great deal of pressure?

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You will know, if it stops it's fecked, if you get covered with confetti its fine.

tomcat59alan said:

You will know, if it stops it's fecked, if you get covered with confetti its fine.

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So it should be impossible to stop the fan regardless of how much pressure is exerted?

If it won't turn at all it's seized.



When cold the fan will be as Wammers has already said.
With the engine turned off & cold mine is stiff to turn by hand initially but as I continue to turn it it frees off to the point of freewheeling.
As things heat up & the clutch works it will become harder. I'd suggest being careful if you want to try that so you don't damage anything.
Bear in mind it uses a liquid to engage so is not mechanically locked together.
If yours does that it's fine.
Mine's a 1986 3.5EFi & I can remove the fan altogether complete with the viscous coupling by undoing the big nut in the centre which holds it onto the nose of the waterpump shaft & fit electric fans such as the Kenlowe instead. The big nut is on the engine side of the vc.
Helps to loosen the radiator shroud to ease lifting the fan assembly out once you've got the nut loose.
The fan can then be removed from the vc. by undoing the four bolts.

I did try the Kenlowe's but noticed b.all difference in fuel economy.
The main difference was the reduction in noise from the engine bay.
I can see an advantage if you do a lot of deep wading as you could fit an override switch to turn them off & not have them fling water all over the engine.

dougc said:

So it should be impossible to stop the fan regardless of how much pressure is exerted?

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It can always be stopped unless it's seized, but you would need to shove a length of 2 x 4 wood in there and it could be destructive

Thanks for all the responses and information. The fan stopped with the use of a newspaper but it took quite a bit of pressure so it looks as if the viscous drive might be on its way out and need replacing.

dougc said:

Thanks for all the responses and information. The fan stopped with the use of a newspaper but it took quite a bit of pressure so it looks as if the viscous drive is on its way out and needs replacing.

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Not sure how you applied pressure, you should use a tightly rolled newspaper and stuff the end into the blades, if it either stops or slows dramatically it's fecked, if it shreds the end of the paper it's OK, engine hot of course.