Thank your Dr. Woitok.
I agree that the heat has nothing to do with the functioning of the VC.  I
am surprised that there are so many people that misunderstand what is
happening in the "mystery coupling".

Joshua Van Tol has the Idea.  The property of a liquid to behave as a solid
is called thixotrophy.  It is simple to observe.  Follow Josh's recipe and
play with the goo.  It is a simple high school experiment.  If you stir, or
pour the goo slow, it will act as a liquid.  If you try to stir (agitate)
it fast, or pour it fast, it thickens up.  Squeeze it in your palm slow and
it will ooze out the sides, squeeze it hard or fast, and it feels like a
solid.

This is why the plates are allowed to slip, the silicone will behave as a
liquid under minimal agitation.  The rear wheels will spin when up on a
jack stand if the speed is kept down.  The liquid is shearing in the VC,
but not enough to make it act as a solid.  More agitation will cause it to
do so.

As far as the life of the VC, I do not see that the fluid could loose it's
properties with age, but contamination from seal failure will definitely
affect it.

I don't think that a company like Porsche would use Viscous Coupling
technology in a 1999 car if it wasn't a good idea.  The complicated ideas
like clutch plate couplings have a lifespan, engineered with friction
surfaces that can wear and fail.  The simplicity of the VC is ingenious.  I
just wish that VW would have given more specific details on
limitations/properties/care of the VC.

I am no expert and all I just said could have come completely from my
imagination, but it seems clear to me, and too many people misunderstand it
and try to make it more complicated that it is.

See ya.
Gary

74 transporter (panel)
78 westy
85 kombi
86 syncroGL