In need of advice on broken bolt

[Blackbeard]

Hi everyone, I'm a newbe so go easy or at least provide some helpful information with a problem involving a broken bolt.
I have a 1987 Yamaha 50 that has been sounding the alarm for overheating. I naturally thought of checking the thermostat to see if it needed to be replaced.
When removing one of two screws, the head broke off of one. I have tried heating the remainder of the bolt, using vice grips and break-free, all to no avail.
I was thinking of getting an bolt removal tool (has reverse threads) but am worried I will wind up breaking the rest of the bolt off. This would not be so bad, but I need to know how much wider I can drill the thermostat housing and tap in new threads.

[rodbolt17]

no need to use a bigger bolt.
either heli-coil it or use the correct 6mmx1mm tap drill and drill it or drill it for 1/4x20.

[Blackbeard]

thanks rodbolt17, will see about getting heli-coil for it tomorrow

[marinermikes]

Just so you know. You don't heat the bolt, you heat the area around the bolt. This makes everything around the bolt expand. Try it and see if it comes out.

[Blackbeard]

Well, I got lucky. I had enough of the bolt sticking out that I was able to get a little larger nut to fit over it (I boogered the threads with my vice grips) and then welded the nut to the bolt. I had soaked a cotton ball in brake-free and left it on the threads/head overnight. This morning I was able to loosen the bolt using the welded nut and wrench and remove it...what a relief.
Thank you both.
PS...marinermikes: how hot do you or can you heat aluminum. Are you talking about a simple propane flame?

[marinermikes]

Good question. I would use nothing but propane on it. Although you can heat aluminum pretty hot I would be very careful not to over heat it. A little at a time and no more than nesseary to get it out. Glad you got it out so you don't have to worry about overheating it. Heating it would be the last resort.