At what temp is the clutch supposed to be fully locked up?

Thanks!

__________________
I'm not a doctor, but I'll have a look.

'85 300SD 245k
'87 300SDL 251k
'90 300SEL 326k

Six others from BMW, GM, and Ford.

Liberty will not descend to a people; a people must raise themselves to liberty.[/IMG]

I take it you're asking about a "thermal clutch fan" and not just a straight viscuous clutch drive fan. The thermal clutch is only sensitive to radiator core temperature at the point immediately in front of it and that depends on the distance between fan and radiator. But, since there's a positive but not perfect correlation between coolant temp at the place it happens to be measured in the engine a properly operating thermal clutch, in my intuitive opinion, I'm not a Pro, the thermal clutch locks up at the point it is designed for, not necessarily coolant temp in the engine. Basically, it responds to heat at the radiator point right in front of it. So, and this is the reason thermal clutch fans are superior, when you're at highway speed there is so much air moving through the core it never locks up, as a matter of fact it just freewheels. When you are stopped and the radiator core heats up the thermal clutch will lock up then, but only fully as the temp goe's past the fans set point. So, the thermal clutch fan only locks up when needed, though it will begin to lock at a point before the engine overheats; it's a gradual thing. If you have a 180 degree thermostat and a matched thermal clutch fan, the fan will be in some state of lockup, but only enough to keep the coolant in the radiator right in front of it at the temp it is designed to do. That's my opinion and I believe it mostly correct regarding therm clutch fans. I'm sure one of the Pro's around here can straighten anything out that needs straightening out.
If you're talking about a straight viscuous drive fan, then that's a different story. The thermal clutch fan is the superior of the two as it reacts precisely the way the engine coolant needs it to react. The straight viscuous drives just begin to further and further lag engine speed, so you risk danger of overheating if you drive it hard in first gear on a hot hot day; not so with the therm clutch.