65 coupe with 327 300hp. How can I test to see if the fan clutch is engaging at high temperatures? I read it should engage around 180 deg. F.

 

Welcome to the forum.

I would use a heat gun and see if there's an increase in stiffness as you try to turn the fan blades. You can usually tell when it engages by the significant increase in fan noise also.

 

Thanks I'll try it if I can get a heat gun to get the clutch to +180 deg. A have side pipes, don't know if I would hear the fan noise. :-)

 

You can get a heat gun at Harbor Freight that will definitely on the high setting get the clutch thermostatic spring to 180°.
I think with the car sitting in the driveway and the hood open, you should be able to notice the change in speed if not the noise level.