Here's a stupid question. But what's the difference in thermal and non-thermal clutch fans?
Also what's the rubber filler you all keep referring to under the front of the car?
I have all the filler under the hood and the lower valance where the fog lights go but just not sure what the other parts is.
Thanks.

Not positive on the clutch fans, but I believe it would be the difference in how they opperate or function. I know newer versions are actually wired as opposed to the older coil spring etc...

The baffels are between the bumper and the core support at each side to prevent air from going around the core support. They are a rubber flexable piece that clips to the support and to the lower valance with special clips...

A few of the repro places carry them now...

Hope you get more specific answers on your clutch fan question...

Brett - 67 Drop Top 455!

Here's pictures the rubber baffles on mine. Scroll down a bit on the page. The right is not clearly visible behind the AC stuff but the left can be seen.
http://www.geocities.com/jims68fb/NoseResto.html

http://www.popularmechanics.com/automotive/sub_care_sat/1772922.html

This may help.

As I remember it, a thermal clutch fan fully engages at a certain temperature, while the non-thermal type _disengages_ at a certain engine rpm.

I don't think they ever fully engage. They have thick silicone fluid inside which allows them to run at less RPM than the pulley is turning, and at higher RPM's they run substantially less than the pulley speed. The thermal ones have the bi-metallic spring that must tighten up something inside so it turns closer to the pulley speed when it feels the hot air from the radiator. I just put on a heavy duty clutch from flex-a-lite. What I don't know is what temperature they activate.