Hello.
From previous posts and the FAQ I have replaced the fan clutch and tested it as follows:

Blocked air flow acroos rad with cardboard, disconnected electric cooling fan and ran car at 2500 rpm. Temp climbs but only to the midpoint (where it always is when running), and stayed there.

I did not hear any roar sound at start up or any time after to indicate the fan had engaged.

Immediately after shutdown, I was able to rotate the fan blades on the shaft in both directions with little or no resistance. As I understand it, the temperature sensor on the clutch should prevent free wheeling from occuring.

So far, this clutch seems no different (looks newer though) from the old one.

Am I missing something, or did I buy a defective part?

I'm not sure the fan should necessarily be on if the car is at operating temp. I've read that the clutch should not be on if there is enough air flowing across to cool it (or it's not hot enough) - the fan should not be engaged, say, when on the highway or moving.

The temp gauge is compensated so you don't know how hot it is unless it's really hot. Try you test again but have the AC on. That should make it hot.

I checked my clutch with the engine cold and there was a fair amount of resistence. I think that is how the viscous fluid settles. I went for a short trip and back and the fan seemed to be freewheeling when I got back. I'm guessing it wasn't hot enough. I'll try the test again sometime and see how it looks when it should be engaged.

Just curious, what prompted you to replace the fan clutch.

There is an good article on the fan clutch in this months (July 2005) Popular Mechanics. I believe it should be on the newstand now.

I would think that covering up the radiator heats the speeds up the test by not letting air cool the thermostatic spring inside the clutch.

What were the spins like on your different tests. My initial tests on mine show my clutch may be spinning too fast...
--
Paul NW Indiana '89 740 Turbo 110,000

This is part of an attempt to optimized A/C performance.

I replaced the fan clutch after reading that the fan should not be able to spin more that 1 turn CCW when the engine is hot (clutch engaged)

A mechanic at an A/C stuck his finger into the fan while the engine was hot and running the the blades immediately stopped, with only a little resitance, indicated the fan was free wheeling on the shaft but the clutch actually engaging.

Seems to be a lot of different opinions on this which is interesting, but I would find it more interesting if my A/C worked better. ;-)

Retest without blocking airflow. And hose out the radiator from the fan side. The fan clutch must have airflow good across the bi-metal coil spring to function properly.