Do you have a power supply large enough to supply the necessary 450W the R9 285 draws? Otherwise, I’m not sure why it is crashing on your system. I have a 750W 80+ Platinum PSU and since then the card has been stable with minor crashes until AMD fully patched them.
Usually the first artifacts are seen at 80°C, with the critical temperature being 90°C and finally the death of ICs being at ~95-100°C (melting)