It was what ever verion of MPS RR had before public release so fairly recent.
I Just installed Heat Gen maxed that out, Heat sinks in every part of he suit, and force feilds until I had full armor. Install the tinker mod for the tool so tyou can adjust on the fly. You cant stay in lava forever but you can defently swim around for awhile and charge your bats.
I stopped doing that after a while. But found a completely diffrent way to freeing super charge the armor. Portal guns and the kenetic gen. Just put a portal some distance away and where you are both on the cieling and then just fly up. Free unlimtied power.
But heat is one of the few balancing things MPS uses so yeah ever update seems to change just how it works (one of the resaons I would have the tinker in the glove) there has been more then once after an update I would have to tweek the heat sink settings. Might be harder to do now dont know have not touched MPS since RR reset there server and went public and don't really plan on picking it back up.