Viscous fans

[Mike D]

Evening folks

I'm after a bit of advice on how a viscous fan is meant to work!

I know it should only start to spin with the engine when it reaches a set temperature, but should it have any resistance to turn when cold?

The one on my 840 seems to have some resistance, and makes the car sound like a big leaf blower, even when cold. I assumed the fan was seized, but it does turn..

Cheers!
Mike

[Lewis]

There's usually a little resistance, as the fluid drags slightly, but it should effectively windmill when cold and be quiet.

Bear with me here. One good trick I learnt, to check for correct functioning, is to get the engine warm (so the viscous is locked up) and then shut it off.

If the viscous is working, it should stop dead almost instantly (as it's locked up, so as the engine stops so does it).

Now, on that basis, if you can do the same when yours is cold - or it at least stops very quickly - I'd be inclined to think there's something wrong with it.

You can also try and feed it a newspaper. I've never done this, but a fan driven by a working viscous coupling should be relatively easily stopped with a rolled-up newspaper.

[composimmonite]

I wonder if you pour a kettle of boiling water over the viscous unit it will increase the "drag" as a non dangerous way of checking if it's working ?
On a van I had one fail so simply drilled though and put a bolt so it locked up solid

paul h

[Mike D]

Thanks Lewis, I shall give that a try

[Mike D]

Right, i've just been out and given it a spin over. car has been sat for 5 hours so is cold..

I can spin it by hand with the engine off, there is a marked resistance though..

When I start the engine, the fan starts spinning and gets faster when revved.. when turned off the fan carries on spinning for maybe a second, then stops..

Does this sound about right? or should it run on a bit longer? When driving it sounds to have a lot more fan noise than it should..

composimmonite, locking it up is the opposite of what i'm after! I have no cooling issues, just a noise one

[composimmonite]

Feb 19, 2012 22:14:47 GMT Mike D said:

composimmonite, locking it up is the opposite of what i'm after! I have no cooling issues, just a noise one

If you confirm that it doesen't lock up when hot by pouring hot water or whatever over it then you know it's knackered and time to replace before hot weather. Rumbling viscous unit is normally a sign that bearings shot and that allows enough movement in seals to let fluid leak out.
Is there any side to side play when rocking the blades ?
If cooling isn't a problem you could try simply removing the fan for a short while and seeing if the noise is actually coming from that.
Another thought,seeing fan attached to water pump, is that pump bearings failing.

Paul H

[jrevillug]

Feb 20, 2012 9:26:14 GMT composimmonite said:

Feb 19, 2012 22:14:47 GMT Mike D said:

composimmonite, locking it up is the opposite of what i'm after! I have no cooling issues, just a noise one

If you confirm that it doesen't lock up when hot by pouring hot water or whatever over it then you know it's knackered and time to replace before hot weather. Rumbling viscous unit is normally a sign that bearings shot and that allows enough movement in seals to let fluid leak out.
Is there any side to side play when rocking the blades ?
If cooling isn't a problem you could try simply removing the fan for a short while and seeing if the noise is actually coming from that.
Another thought,seeing fan attached to water pump, is that pump bearings failing.

Paul H

I don't think the noise is coming from the pump/viscous unit - more the huge quantity of air being moved.

[Mike D]

Aye, it's the air noise rather than any sort of mechanical noise..

I might just buy a new unit anyway, they're 35 quid and if it doesn't eliminate it it must just be how it is - i'm pretty sure the unit fitted is a bit 'stiff' , i'm just feeling a bit wimpy stuffing a newspaper into it!
Maybe I just need to man up!

Cheers for the help gents