I have this happening on a few machines I have tested it on (All ATI GPU's but not sure if its just an ATI problem) but its extreme on my main gaming laptop (Asus G73) with an ATI 5870 in it. I think I have Catalyst 12.1a preview drivers on it currently - as that's what I use to make sure ID software's game RAGE runs properly. I just recently had the fans cleaned in this machine also after it overheated and shutdown trying to play Grimrock.
You can check your GPU's temperature with software like GPU-Z. My laptop when it plays Crysis, RAGE, Skyrim, Batman AA & AC the maximum I ever see it at is about 82 degrees but usually no more than the mid seventies. When I play Grimrock it shoots up too just over 90 degrees and is very gradually climbing. When I am not playing games the temperature is usually 45-55 degrees (I live in a hot country I should mention). I have tried Vsync on/off to no avail also and this is as soon as you start a new game in the very simplest dungeon room.
I'm also a games programmer by trade and lots of my own work stuff that _really_ maxes out my graphics card in that machine doesn't cause such problems and even other simpler 'work stuff' with reasonably complex shaders that runs at frame rates in the range of 1000fps+ unlimited doesn't seem to cause this issue on the same machine.
Otherwise a cool game I would love to be able to properly play
EDIT: Also I want to try the new FPS limit option that I can apparently put in the CFG file but I don't see it there? (Steam version btw)