RR Viscous Fans

How do you know the Viscous Fan is working? Can you test it? How much do they lockup?

My 1990 RR viscous fan is quite happy to be rotated when the engine is cold and not running.
I am not convinced that it locks up when [in my case] the temperature gauge was near the red part of the temperature gauge.
I stopped the engine and the viscous fan had negligible resistance to be rotated as above.
Only happens under big power loads, has new radiator, water pump, thermostat, clean block etc.
Thankyou in advance, John

"Milcom Instrumentation" <[email protected]> wrote in message
news:[email protected]...
How do you know the Viscous Fan is working? Can you test it? How much do
they lockup?

My 1990 RR viscous fan is quite happy to be rotated when the engine is cold
and not running.
I am not convinced that it locks up when [in my case] the temperature gauge
was near the red part of the temperature gauge.
I stopped the engine and the viscous fan had negligible resistance to be
rotated as above.
Only happens under big power loads, has new radiator, water pump,
thermostat, clean block etc.
Thankyou in advance, John



I read somewhere that you should do a 'carrot test':- With your engine
running cold, shove the carrot in the fan blades and it should stop it. Try
it when it's hot and the carrot should be sliced. Seems reasonable to me.

My RR classic was overheating recently so I tried stopping the fan with a
stick (didn't have a carrot to hand) and it stopped way too easily. I
concluded the viscous clutch bit was knackered, took the central fixing nut
and washer off, added a large repair washer, which spanned the loose bearing
part, whacked the original washer and nut back on and now it's locked
permanently on. Makes quite a noticeable airflow roar even at tickover. Not
a sensible solution if you want proper temperature control or fuel economy
from your RR but it suits my needs.

HTH
Peter

On or around Tue, 26 Apr 2005 23:18:03 +1200, "Milcom Instrumentation"
<[email protected]> enlightened us thusly:

>How do you know the Viscous Fan is working? Can you test it? How much do they lockup?
>
>My 1990 RR viscous fan is quite happy to be rotated when the engine is cold and not running.
>I am not convinced that it locks up when [in my case] the temperature gauge was near the red part of the temperature gauge.
>I stopped the engine and the viscous fan had negligible resistance to be rotated as above.
>Only happens under big power loads, has new radiator, water pump, thermostat, clean block etc.
>Thankyou in advance, John

FWIW, according to my experience with the 2 I've had that actually work
properly:

initially, when you fire up the cold engine, the fan spins. After about 20
seconds or so, it slows down to idle - you'll hear this happen, especially
if you're running moderately high revs - the fan's noisy when it's running.
(actually, tell a lie, the 300 TDi one works as well)

On the sierra, the fan doesn't come back in again until the engine's quite
hot - the only time I really noticed it do its thing was when tuning the gas
system, which involves running it at about 3000 rpm with it standing still -
after a few minutes, that makes it hot; and I did actually verify that the
fan kicks in again - although only for quite a short period.

--
Austin Shackles. www.ddol-las.fsnet.co.uk my opinions are just that
If all be true that I do think, There are five reasons we should drink;
Good wine, a friend, or being dry, Or lest we should be by and by;
Or any other reason why. - Henry Aldrich (1647 - 1710)

>
> >How do you know the Viscous Fan is working? Can you test it? How much do
they lockup?

I've never managed to get mine hot enough to need the fan, even though the
diesel pump's turned up and even when towing the boat.

TonyB

"Austin Shackles" <[email protected]> wrote in message
news:[email protected]...
> On or around Tue, 26 Apr 2005 23:18:03 +1200, "Milcom Instrumentation"
> <[email protected]> enlightened us thusly:
>
> >How do you know the Viscous Fan is working? Can you test it? How much do
they lockup?
> >
> >My 1990 RR viscous fan is quite happy to be rotated when the engine is
cold and not running.
> >I am not convinced that it locks up when [in my case] the temperature
gauge was near the red part of the temperature gauge.
> >I stopped the engine and the viscous fan had negligible resistance to be
rotated as above.
> >Only happens under big power loads, has new radiator, water pump,
thermostat, clean block etc.
> >Thankyou in advance, John
>
> FWIW, according to my experience with the 2 I've had that actually work
> properly:
>
> initially, when you fire up the cold engine, the fan spins. After about
20
> seconds or so, it slows down to idle - you'll hear this happen, especially
> if you're running moderately high revs - the fan's noisy when it's
running.
> (actually, tell a lie, the 300 TDi one works as well)
>
> On the sierra, the fan doesn't come back in again until the engine's quite
> hot - the only time I really noticed it do its thing was when tuning the
gas
> system, which involves running it at about 3000 rpm with it standing
still -
> after a few minutes, that makes it hot; and I did actually verify that the
> fan kicks in again - although only for quite a short period.
>
> --
> Austin Shackles. www.ddol-las.fsnet.co.uk my opinions are just that
> If all be true that I do think, There are five reasons we should drink;
> Good wine, a friend, or being dry, Or lest we should be by and by;
> Or any other reason why. - Henry Aldrich (1647 - 1710)




This has made me worry now.

My fan is stuck on permanently. It will not move, only when the engine turns
it. It increases with engine speed and stops as soon as the engine stops.

Do i need to get a new viscous unit?

On or around Thu, 28 Apr 2005 10:12:03 +0000 (UTC), "Mark Solesbury"
<[email protected]> enlightened us thusly:

>
>
>This has made me worry now.
>
>My fan is stuck on permanently. It will not move, only when the engine turns
>it. It increases with engine speed and stops as soon as the engine stops.
>
>Do i need to get a new viscous unit?
>

that depends if having a full-time fan bothers you.

You waste a bit of energy and create a bit more noise; if either of these
are a problem...

there again, a seized hub is preferable to one that fails free so that the
fan doesn't spin when it should.


--
Austin Shackles. www.ddol-las.fsnet.co.uk my opinions are just that
"The breezy call of incense-breathing Morn, The swallow twittering
from the strawbuilt shed, The cock's shrill clarion, or the echoing
horn, No more shall rouse them from their lowly bed."
Thomas Gray, Elegy Written in a Country Churchyard.

http://www.jag-lovers.org/xj-s/book/FanClutch.html
www.lrx.com/forum/messages/12364.html

Thankyou for all those replies. I purchased a aftermarket viscous hub for $200nzd [half Rover's price] and all is well.
My old hub was stuffed. Just sat there and free spun as if it was working!
What is interesting is they are very hard to test.
It was obvious on mine after the new hub was fitted it pulled so much more air after a hot run; that is holding your hand behind the fan and feeling the amount of air.
The carrot test is possible the best test, although I have not tried.
In my case I towed the caravan again up a large hill after fitting. No problems and the gauge remained on 3/8th fsd which is perfect. I stopped the engine and expected to find the viscous fan locked up...wrong , nice and free [but it had been working]
These things are very clever.
They need to be spinning to work.
They do have a pump inside.
From cold they do lockup [only when spinning] for 40 seconds until the pump pools the oil back into the centre hub.

I believe mine had either lossed its oil? or the second bi-metallic valve had possibily stuck open and allowed the oil to pool back into the centre hub.

The above message 12364 has a good explanation and the
Jag-lover has good pictures of what is inside.
Thanks, John