My temp is fine in any weather until I turn on the A/C. Usually gets pretty hot when I'm on the highway. I don't know if would actually overheat because I turn the heater on when it gets between 2/3 or 3/4 of the way up on the guage, then it jumps back down within a minute or so. Are the fibers something that are easily visible? I was thinking it could be my heater core, but I never notice an antifreeze smell, just sometimes a musty smell when I hit the A/C. One other thing- Could the fact that I think the A/C needs to be recharged have an effect on the tempurature of the engine? A lot of questions, but I would like to take the SHO down to TX in Sept. instead of our Blazer but I'm not going to risk overheating out in the middle of nowhere.