I've been having issues with my Powercolor 6970. At around 85-87c the screen goes black for 5-10 seconds, and windows notifies me that the graphics drivers have crashed and recovered. I can reproduce the problem in furmark and just about any game that stresses the card enough to produce those temps.
I've maxed the fan speed in overdrive, and both fans on the heatsink are working. The heatsink is clean, too. I've taken off the side panel and pointed an oscillating fan at it, and it still reaches those temps. The card is about 6 months old, and hasn't had this problem before. It seems a bit odd the temps would get that high if both fans are working, there's plenty of room temp (75 F) air circulating around the card and the heatsink is clean. From what I've read the max temp on a 6970 is ~100c, so I'm not pushing its max either, though it probably would if the drivers didn't crash, the heat graph is more linear than parabolic.
This is also on a fresh windows install, without overclocks. I reformatted to help isolate what the problem was, so it's been doing it before and after the new install. Any tips would be great.
I reseated the gpu cooler with ic diamond, dropped the temps ~20c. It maxes out at about 70c with the fan at 65% in furmark 1080p burn in now. Maybe the heatsink started coming loose after all this time... In either case, it's more or less fixed with some expensive tim and a simple reseat.