I did this once. And then broke the easy out in the bolt. So we drilled the thrmostat housing for a new bolt, and drilled and tapped the head for a new bolt. If you get stuck, you may have to try relocating the stud in this fashion. You don't need to pull the head or anything. You could also try making a bigger hole around the current stud, but I am not sure how much meat is there before you run into a water jacket. If you do this, you would end up with a big stud on one side, but that is OK.

Philip

I'm with Aye Roll if you can find a "left handed" drill bit try that first. I have had much better luck with them rather than ez outs. They my be a little hard to find tho. I'm lucky to have oil field supply stores close by for things like these and high pressure hoses and such. you can most likly do this yourself but don't break an ez out off or then it's probably going to take a machine shop to get it out.
Bret
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rust free in west Texas

I am not familiar with the setup, but it sounds like this is a stud that is screwed into the head and then a nut is used to make the seal on the thermostat. Easy outs are great when they work as designed. It is necessary to drill in the center of the stud. If enough stud is exposed you can begin by filing the surface flat and carefully using a center punch to produce a starting point for your drill. The real problem arises when you break an easy out off. They are hardened and extremely difficult to remove when broken off. Use common sense on how much force you think the easy out can withstand before it might break. Buy quality easy outs- the no-name Chinese ones will probably be trouble makers.

You might explore the possibility of drilling out the stud and tapping the resulting hole if it is just slightly bigger than the current stud. You might find a fractional size that would be a little bigger than the current metric. Good luck.

Randy

Gary
You can try to fix this yourself, if all goes right your okay if it fails to you need to have the hole rethreadded.go to your local auto supply store and ask for a set of Easy Outs, they should know what they are, basicly you take a drill bit and drill a hole through or half way through the center of the broken bolt, you then take the easy out ( which screws the opp of screws ) put that in the hold you just drilled and go in reverse , the easy out should screw itself into the bolt and start backing the broken bolt out of the hole. its that easy.