Sounds like you have an issue there, maybe the heat sink has come away from the card or it could just be full of dust. Dust is a computers no 1 enemy. Have you opened it up and had a look ? If not do so and carefully check the blades on the fan and if there is a lot of dust there then clean it CAREFULLY. Anyway at the performance level of the 8600 you shouldn't really get heat issues, if you do the card isn't cooling properly.
Heat starts to be an issue with higher tier cards especially top end cards as they draw a lot of power or mid to high end cards if in a multi card set up.
Check the card first then get back to us and list system specs/budget and what you want to do with a new card, mainly gaming ? or some video playback ? Then we can recommend something to suit.