V8 Saloon Viscous Fan - suspect not performing correctly

[KV8]

Hello.

This is a follow on from my thread concerning noise level in my car. A major component of the noise seems to comprise a "roar" .

Having now somewhat eliminated the exhaust I have now thought of another possible source of this type of noise.

Is the viscous fan coupling working OK? - or is it remaining coupled at high revs causing an air inrush roar.

When static, flicking the fan results in it turning a couple of blades it is however stiffer than the viscous fan on my Triumph Stag.

On Youtube there are several videos of guys simply stopping a viscous fan from 2500 - 3000 revs by inserting a rolled up magazine,

I set the engine to 3000 rpm (by placing a brick on the throttle pedal). Inserting the rolled magazine just created a snow storm of paper flakes.

Furthermore increasing the revs still further seemed to increase the air flow even more.

BTW I remember that Russ Carpenter said something about the viscous coupling on my car being non standard and was a far better one from a Buick!

Any comments on the above or suggestions as to further tests greatly appreciated.

Thanks

H

[Sydsmith]

Howard, I am sure you will know that when the engine and fan are cold the fan will turn freely, as the engine warms up the viscose coupling stiffens up and the fan increases in speed.

So the magazine test will only work when the engine is cold and in my experience that is not very long after the engine of my V8 250 has been started, even with the bonnet up.

You will also know fans are designed for a particular car and are rarely interchangeable, even if they mechanically fit. With due respect to Russ, I am not sure how a fan from another car could be better than an original fan designed for a V8 250 working properly.

Like radiator caps they all fit but they all do a different job.

My first V8 had the fan glued to the boss because the coupling had failed, as you say, it roared at any sort of revs, I think you have found your noise problem. Syd

[KV8]

Many thanks Syd

I did not know that the performance of the viscous coupling changed with temperature. The top of the radiator was just warm when I carried out the magazine test. (I leaned on it with my left hand whilst carrying out the test).

From what you say do I gather that you think my fan is not slipping as it should at high revs thus contributing to the noise level?

So where do I go from here? Fit new viscous coupling? Can this be done without removing radiator and cowl?

On inspection it appears that whilst the fan can be removed without removing radiator and cowl, refitting with these still in place could be a can of worms. Once removed should I consider a Kenlowe or similar instead?

Thanks again

H

[tjt77]

you can always remove the fan assy and briefly run the engine without it to help identify source of noise.. IF it IS the fan.. and you find the noise produced irksome, you can always fit an electric fan and thermostat switch to control it.. almost all modern cars have no mechanical fans on them today.. partly due to space and partly due to the desire to reduce noise..

[Christopher Storey]

To test whether this is the noise source, there is no need to remove the fan . Slackening the dynamo/alternator belt and disengaging it does not take long, and with it removed you can safely run the engine for the 60 seconds or so that you need to rev it up and listen

[KV8]

Thanks for your interest.

However I do not see how slackening the alternator belt would have any effect on the fan? The fan is mounted on the water pump spindle and driven from the crankshaft pulley via the belt tensioner. The alternator is driven from a second pulley on this Water pump / fan) spindle.

Regards

H

[Christopher Storey]

Well if yours is dual drive it is even easier : just push the tensioner in towards the block and then ease the belt off the 2 pulleys . You may need to slacken /remove the alternator belt also, ( I do not know because my car has a dynamo ) but the point I am making is that there is no need to take the mechanical parts such as the fan off to do the test which is envisaged

[KV8]

Many thanks

I thought all Daimler V8's were dual belt drive? (even before "owner" dynamo upgrades to alternator)

However as you point out removal of the belt drive from crankshaft to fan pulley is actually simple. However since this would also remove the drive to the water pump would it be safe to run the engine to test?

TIA

H

[Christopher Storey]

Oh yes, there is no harm in running the engine for a short period , by which I mean up to perhaps 60 secs which will be ample to tell you whether the noise has disappeared . I would not go beyond 3000 rpm

You are quite right of course that even with a dynamo the primary drive is from crank to water pump !