viscous fan

[len]

hi. should the viscous fan offer any resitance when spinning by hand ? i have not got any problems but i often seem to remember on another Stag that i use to have it seemed to cause a big draught at times when starting etc, but the one i have now doesnt, what the easiest way to define if its working well ?
Len

[DJT]

Len,

The VC should have resistance when spinning by hand. It is designed to run at engine speeds up to just shy of 3000rpm when the viscous fluid allows it to slip. Spin it by hand and it should stop within a couple of blade widths.

[Kevin Garrod]

Yes, when you try to spin it, it should stop quite quickly. Mine stops after less than half a turn.
It should not spin freely nor should it be solid.

[martin]

Hi Len, I hate the bloody things, mostly because there's no definitive way of testing them. Take hold of a blade about half way down its length, and see if you can detect any movement, any at all, in the bearing, if you can, replace the thing before it trashes the rad. As the others say, it should only be free for a couple of blade widths. It should be one of those things you can test by replacing, sadly they're too expensive for that. I got a good'n from Bob Heritage on the strength of my doubts, and it was a good move. Sorry for the vague answer. Martin.

P.S. I thought of locking it up, but because of the design of the blades, they curve forwards and hit the rad.

[V Mad]

Actually there is a way of testing the viscous coupling. As Dave says there is a max speed figure which the fan should not exceed. This prevents the fan drawing excessive power from the engine and also

I bought one of these hand held tachometers which measure the rotational speed by reflecting a laser beam off a rotating surface. Just stick a reflective sticker on a blade, run the engine up to over 4000 rpm. The tacho reading should not go over 2800 (or whatever the viscous spec is, I dont recall exact figure. It should also not be too low either, again I cant recall the figure off hand).

Len, if you dont feel a good strong draft of air when revving the engine (you should hear it too) then viscous coupling needs replacing.

[len]

thanks for replies
will check again in morning, but am pretty sure it will spin a fair distance before stopping, cant say i recall hearing the draught when starting up. i reckon its us .
len

[len]

have had another look at viscous fan today and i would say it would spin a full revolution with mininum effort, so am going to invest in a new one.
Len

[wilf]

Len, surely better to fit an electric fan and be done with it? Just a thought.

[len]

hi
could do that . but to be honest have not had a problem with the original set up . even on my first Stag back in the 80 s ,so will stick with it.
i must admit i use to worry about oil pressure and the temp all the time , but now i rarely glance at these ,
Thanks for giving me a word of advice though,
regards
Len

[ChasR]

You seem to get many opinions on how to check a VC

On my Dolomite Sprint (which according to the part numbers shares the same viscous coupling as a Stag) it had a new item only a month or two prior to me buying it. Whilst according to the advice my Stag one is fine (if you spin it by hand it will continue for a couple of blades width until it stops whereas a few I have seen would continue on for over half of the fan's circumference) the Sprint VC would turn a little stiffer by hand in addition to coming to a halt as soon as you let go of the fan. You could also hear the fan spin slightly (the wind noise) when initially blipping the throttle from idle, something not present in the Stag.

[Moraystag]

If the VC is on it's way out would it cause a small rise in temp I seem to be running a little warmer however the last time I was home the outside temp was about 22-23 c
Maybe a bit of paranoia, but when sitting at junctions or lights the temp gauge deffo moved from between the E & M to M.

mIKE