confused with viscous fan

been to a independant Landrover garage today to get the three amigos sorted

well as the drive belt was screeching i asked them to replace it whilst it was in.
they told me that the viscous fan was seizing, hence a wurring noise,
ok so here's the confusion. how can the viscous fan seizing cause the belt to slip? i'm thinking it must be the idler pully?
and if it is what's it like to change it?
Rave and Haynes manuals don't even mention the idler pully.
many thanks

sparky steve said:

been to a independant Landrover garage today to get the three amigos sorted

well as the drive belt was screeching i asked them to replace it whilst it was in.
they told me that the viscous fan was seizing, hence a wurring noise,
ok so here's the confusion. how can the viscous fan seizing cause the belt to slip? i'm thinking it must be the idler pully?
and if it is what's it like to change it?
Rave and Haynes manuals don't even mention the idler pully.
many thanks

Click to expand...

I suppose it could as it will be runnung all the time and won't do your fuel consumption a lot of good.
Simple test, can you rotate the fan with the ENGINE OFF ?

We're talking Td5 here I assume?

Not overly familiar with the Td5, but it makes sense to me that the viscous fan is attached via the water pump? In which case I would say that it is the idler pulley that is causing the problem. If it is siezing then the belt will be forced round by the water pump but as the idler is not rolling the belt will slip over it causing a squeel.

crazymac said:

We're talking Td5 here I assume?

Not overly familiar with the Td5, but it makes sense to me that the viscous fan is attached via the water pump? In which case I would say that it is the idler pulley that is causing the problem. If it is siezing then the belt will be forced round by the water pump but as the idler is not rolling the belt will slip over it causing a squeel.

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sorry yes it is aTD5
the water pump isn't driven off the drive belt on the TD5??
it seems to have an idler pully, that's if i'm right??
and i'm presuming that it's starting to seize.

OK, it does make sense that its the idler pulley though.

Lets face it, the viscouse fan is SUPPOSED to sieze isn't it!! Thats how it works!

The viscous coupling to the fan allows an amount of slip so that the fan can run slower than the engine. As the engine speeds up the fan will require more power to spin so the coupling will slip more and the fan will only go a little faster. When the coupling is cold it can slip quite freely and the fan will spin quite slowly but as it gets heated by the air flowing over it from the radiator it will become tighter and the fan will turn faster.

If the viscous coupling is seized then the fan will have to spin at full engine speed requiring a lot more power from the engine than it normaly dose and this could be more power than the belt can provide causing it to slip.

With the engine off you should be able to turn the fan by hand fairly easily and it should feel like there is a spoon in soup attached to the other end when the engine is cold and mote like stirring porridge when the engine is hot. If its grinding at all or very hard to move I would ditch it and fit an electric fan.

If the fan seizes up at speed the sudden torque will cause the belt to slip

I recently changed the fan on a td5 that was completely seized.

Even stuck it in the vice to demonstrate to the customer and that ****er was seized solid!

However, there was no sign if any belt squeal or slip.

So I wouldn't say the fan was the cause unless you had a weak tensioner. A seized fan makes a jet engine kinda sound, not a squeal.

Either weak tensioner or knackered/gone shiny belt, which isn't gripping the pulleys so well. Or a bad idler bearing running out of true?

many thanks for all your replies

update

i've tried to turn the fan by hand, and it turned quite easy,like truning treacle, and looks new,clean and shiny.
had a new drive belt on the car on thursday,which the garage struggled to get on so i don't think there is a problem with the tensioner.
the old belt looked ok but was glazed on the none groved side.

the screech sound is still there (but not as bad) as i acclerate comes in around 1500>2500rpm. as soon as i let off the power the noise stops.

would it be worth taking the fan off and see if the belt still slips?

so it does look like it's the idler pully/bearing, so how the heck do you change it? is it just a bearing or does it come with a housing?
i can't find any info on this part..

Take the belt off again (I think it's a 15mm spanner you need on the tensioner to ease it off again against spring tension) and then check every pulley and idler.

Check the power steering, alternator, the lot. Check for rough turning, lumps and stiffness, also wobble in the bearings etc, see if any of the pulleys are running out of true.

Also, run the car with the belt off for a short time just to check it is actually the belt!!

Mr Noisy said:

Take the belt off again (I think it's a 15mm spanner you need on the tensioner to ease it off again against spring tension) and then check every pulley and idler.

Check the power steering, alternator, the lot. Check for rough turning, lumps and stiffness, also wobble in the bearings etc, see if any of the pulleys are running out of true.

Also, run the car with the belt off for a short time just to check it is actually the belt!!

Click to expand...

OH **** please don't go there!!!!

would this be the part i need? ERR5285. ROLLER BEARING VISC FAN TD5 DEF/DIS11(P)
from Britcar web site

http://www.brit-car.co.uk/product.php?xProd=175795

i think i've got it sorted
here's how to change the bearing
http://www.landyzone.co.uk/lz/f8/how-replace-td5-viscous-fan-bearing-122390.html