I have two 15+ yr. old vehicles with viscous fan clutches - one in my sig.

My experience has been they're working when they lock up at shutdown when the engine is good and hot. It gets HOT where I live from late April to early Oct. Lots of opportunities to test a VC.

I believe the OP is in Wisconsin.

If I'm right - it will be a long time B4 a WI car equipped with a VC can be tested.

With winter here - I'm not too sure I'd worry about it that much.

__________________
Mike Murrell
1991 300-SEL - Model 126
M103 - SOHC
"Fräulein"