I have an original 68 396/375 Camaro fan clutch that I'm not sure is working properly (engine overheating at idle). I'm concerned that the "fluid" has run out the front side of the fan. Does anyone know what this fluid is, how much it holds, and where one could purchase the fluid? It also might be useful if someone could describe the proper operation of the fan clutch and how you can be sure when its not working properly.

Same thing happened to my 1969 this past summer. It definately sounds like a fan clutch (assuming you haven't removed the fan shroud, etc.). I believe the fluid is a silicone base....

Unless you are a stickler for originality (ie- trailer queen) I would say...jog on down to the auto parts store and buy a new one for $30-40.

RS,
Usually a good test of the clutch is to go for a ride and get the motor good and hot, stop and let it idle for a minute or so and then shut the motor off while someone watches the fan. It should come to a stop within a revolution or two when it is hot. If it spins free for a while before it stops, the clutch is probably bad. This is sort of a subjective test. If you have a known good fan to watch, use that as a comparison.
The fluid is some sort of silicon substance and I do not beleive it is servicable. Like mccorry said, a new one is cheap, I would just replace it if it is bad.

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Bill Koustenis
Advanced Automotive Machine
Waldorf Md