viscous coupling working?

[Dieter H. Marschall]

Hello everybody, I have the feeling that the VC in my Stag is not working (properly). When I turn it with a cold engine, it spins about 1/4th of one turn. When the engine is hot, it does only the same. Do you think it is broken? Among my spares I have three more used VCs. How can I check whether they are working properly without having to install them? I was told that you have to store them in an upright Position - which I did. Kind regards, Dieter.

[robbo]

Hi dieter.
Mine spins a 1/4 turn when cold with a nice oil damped feel (don't know how else to put it)but I haven't checked it when hot. My car has no overheating problems so I always assumed that all is ok. Sorry I can't be any more helpful
Regards Rob

[milothedog]

Not brilliant, mine will spin 2 blades at most when the engines is stone cold

Ian.

[DaveB]

Mine was spinning about 1/2 turn. Replaced with new one from Bob, now only spins about 2 blades cold, and engine running about 5 deg cooler than before.
Dave

[V Mad]

Dieter, the visocus coupling is not intended to be heat sensitive, so the fact that yours does the same when hot and cold is no indication of failure.

[milothedog]

Rear-wheel drive cars with longitudinal engines usually have engine-driven cooling fans. These fans have a thermostatically controlled viscous clutch This clutch is positioned at the hub of the fan, in the airflow coming through the radiator.

Ian.

There are 2 types, torque type & heat sensitive, I'll put my reply down to the 3 pints of Youngs Special and Wine I had last night before we came home and thinking generically and not specifically Stag It still shouldn't slip too much though as it will reduce it's efficiency.

[wilf]

My understanding is that the Stag viscous coupling is not heat sensitive. It is there to limit fan rpms. Discuss.............lol


Edit: but try not to fall out over it...........

[ChasR]

Indeed, I was under the understanding that the Stag VC was a rev limiting device for the fan, hence it being also call a Torquadrol in some literature (or something to that effect) .

[martin]

Dieter, the visocus coupling is not intended to be heat sensitive, so the fact that yours does the same when hot and cold is no indication of failure.

?

[KOY 23]

Martin.
Must not mock, he's right for once, apart from spelling.

[jleyton]

I'm sure I have read in Triumph literature that it is intended to limit the speed of the fan to 2,500 rpm.

Cheers

Julian

[Dieter H. Marschall]

I'm sure I have read in Triumph literature that it is intended to limit the speed of the fan to 2,500 rpm.

Cheers

Julian

Hello everybody. What Julian wrote is what thought, too: This VC is supposed to limit the revs of the fan, so that the fan is not sucked into the radiator. So what does the viscous stuff do inside the VC? Best wishes, Dieter.

[Westfaling]

Dieter
The viscous fluid allows the fan to slip at higher engine RPM. It reduces power draw. The ram air effect at higher vehicle speeds is theoretically supposed to provide sufficient cooling.
I've never seen anything that indicates that there's any thermal element to the Stag viscous coupling operation.
Regards
Nick

[wilf]

What the thing does is limit torque by slipping, a simple way to limit fan rpms as the torque a fan needs to drive it is directly proportional to its speed (square law IIRC).

The reason it has fins on its external surface is because the action of slipping creates heat, which needs to be conducted away in the airstream.

Viscous couplings in other applications, such as differentials or 4WD couplings, act in the exact opposite way- they slip to begin with, but lock as more torque is transmitted. Confusing old world, ain't it though?

[72BLUE]

I used to work with the guy that designed the VC, previously he worked for a company named Holsett up in Yorkshire. He did tell me that he held some sort of patent on the fan design. Years ago when my Dolly Sprint VC failed, he said he had some of the fluid at home and offered to repair it!

Cheers
Keith