i'm sure this has probly been asked before but...
do plasma weapons on obliterators overheat?

Yes. No rule states that they do not.

The only plasmaweapons that don't overheat are those mounted on vehicles.

oh well at least my obliterator didn't kill himself for nothing then :P

yeah, I once lost an oblit to an over heating twin linked plasma gun, that's like 3 one's in a row. I placed that die in the middle of all of my other dice and lit it on fire as an example to the others. :o

as others stated they do over heat but remember if youre using the plasma guns they are twin linked so you can possibly avoid it. and there is no overheating on a 2 anymore if you rapid fire in 5th ed. so no matter how many shots you cook off you only over heat on a 1. which is much better than that 1 or 2 stuff in 4th ed.

yeah i had a dice like that once, i put may other dice in a circle around and repeatedly beat it with a hammer. that one dice is now 17!!