Changing thermostat (94 s10) HELP!?

Got the corroded thermostat out but bottom bolt will NOT budge. Head of it broke off, tried liquid wrench no luck...help!!! Ideas?|||if theres a bolt stuck i%26#039;d try hot candle wax to get it out. i know it sounds weird but if you drip hot wax from a candle on it, it might come out.