Viscous Coupling

[seaside bill]

Just got mine back together after the viscous coupling failed and have been out on the inaugural run on quite a warm day. Wow, what a differerence a new one makes! The amount of air being shifted around is muchgreater than previously, plus I'm running about a needle width cooler than before. Until the bearing started to disintegrate, mine seemed fine, but obviously not as good as it could be. Previously I'd done the usual checks, but the replacement will only rotate throughabout 1 blade if you spin it by hand as opposed to3 or 4 blades on the old one.

It seemsto me that they lose effeciency over time - 30+ yearsof spinning is a long time- so maybe worth changing every now and then like timing chains?

[Kevin Garrod]

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If I give mine a good flick it spins about 1/2 a turn or less, certainly more than 1 blade, it may be the cause of an intermittant squealing that I'm getting, not sure, I reckon I'll be fitting an electric fan soon and doing away with the original.

The car doesn't run too hot though, if I get stuck in a traffic jam after driving at motorway speeds on a hot day the needle moves to the edge of the red, so I switch the heater on full and turn on the blower and it goes no further. I guess that's 'normal' for the stag with its 'marginal' cooling system:?

[saffronstag]

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Tried mine and couldn't turn it more than1 & 1/2 blades however hard I flicked it.

Not certain when but imagine it must have been replaced at some point in it's 35 years.

[Paul Goldsmith]

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My old viscous coupling didn't seem excessively slack, it would spin under 1/2 a full rotation when flicked by hand. Trusted advice was that this was fine and not contributing to my ongoing errant engine temperature .

Also, I had no noises when running but when pulling the viscous fore & aft there was somemovement and a dull 'click'. I've since been told this can be a sign of a viscous starting to fail.

With temperature still causing concern and having tried everything else to no real avail, for the sake of £55 I thought I hadnothing to lose.

Wow !!! Does my new viscous make a serious difference, step out of the car with the engine idlingand you really notice the warm air blowing out from underneath the Stag. Also open the bonnet at tickover and there's a impressive draught - so much so, I'veneededto ensuremyhot air pipe is firmly inserted below the air filter !

Now, the fan only spins less than one blade width and there is nofore-aft movement evident on the viscous.

The replacement viscous,combined with aminor timing adjustment & mixture correction, my running temperatures are now ranging 1/3 to 1/2 (two dots position) down from 2/3 to 3/4. So I'm well pleased !

For such a small cost and from what I've personally experienced, replacing a tired viscouscertainly shouldn't be overlooked if temperatures are starting to rise.

[chrisn]

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What is it about the viscous unit that 'goes' when it fails? Is it a bearing, and if so could this be replaced rather then forking out for a whole new unit....

[seaside bill]

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Chris

Iunderstand theunit contains silicone fluidwhich transmits the drive to the fan - probably difficult to remove the bearing while retaining the fluid?

It may be that the silicone fluid loses some of its viscosity over time orleaks reducing the efficiency. I'm not convincedthere's anymajor benefithaving one fitted to a Stag given its marginal cooling characteristics. As I understand it, the only function of the viscous coupling is to savethe fewbhp needed to drive the mechanical fan when cooling is being achieved at higher revs by the ram effect of air forced through the radiator.

[chrisn]

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Bill

Thanks. I understand the principle involved, its just that I prefer to renovate an original component rather than ditch it, if it is safe and practical to do so. I don't imagine that bearing will also seal the fluid in, but I can see that the fluid properties might deteriorate with time.

[DJT]

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Bill,

Thanks for the posting. I took your advice and checked mine. It spun for over a full revolution when given a flick. Fortunately I have a spare on the shelf as mine is Mk1 and no longer obtainable. Fitted it this morning, took an hour from start to finish, and now it only turns a couple of blade widths when spun. Sounds more efficient too. No all I need is for the rain to stop to give it a proper test. In the recent warm weather mine has been reading just under 90 degrees on the gauge (just below half with 88 degree 'stat), rising to 90 degrees (exactly half) in traffic.

Forecast for sun this afternoon, so will be able to give it a try.

Dave