RR Viscous Fans

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" enlightened us thusly:

not running.

near the red part of the temperature gauge.

rotated as above.

clean block etc.

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.

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

cold and not running.

gauge was near the red part of the temperature gauge.

rotated as above.

thermostat, clean block etc.

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" enlightened us thusly:

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.

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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.=20 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=20 Jag-lover has good pictures of what is inside. Thanks, John