Well, if you broke the bolt and its half way out you can try to get a good set off vice-grips and clamp that sucker real good and try to twist it off, if its deep and unable to get too, you might want to opt for a extraction tool which is a bit that you can insert into a drill and back it out. Look something like this: http://www.google.com/imgres?um=1&hl=en&sa=N&biw=1024&bih=639&tbm=isch&tbnid=jp_-Z5A2FPH1PM:&imgrefurl=http://www.ebay.co.uk/itm/Broken-Sheared-Bolt-Extractor-set-6-12-mm-Stud-/310092247589&docid=JVw9gFEMyTWB5M&imgurl=http://hdtools.co.uk/family/albums/album50/Boa_Bolt_Stud_Broken_Extractor.jpg&w=388&h=378&ei=pecuT9LZEo-48gPr3JiBDw&zoom=1 Good luck and keep us updated, btw grab a new thermostat and housing if possible from a junkyard, if your cheap like me. check local part stores if you are in a hurry. Extractor should also be available at home-depot/ advance auto ect. call and ask before driving there, save gas.
