So I created a forum account just to post this, since this addon has been pretty impressive so far. I started testing thermal rockets out and for about two hours I couldn't get them to work. I noticed that after I activated them, fuel lines were good, attached to a reactor but it would produce a flame-out animation and just stops working. In fact, my KSP wouldn't even let me throttle up. Peculiar! After two hours, I figured out it was because I have Mechjeb's prevent overheat turned on and it prevented the thermal engines from throttling at all. So for anyone else using Mechjeb and utilizing this particular feature... Turn it off