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Daryl, Shop Owner, Certified Mechanic
Category: Car
Satisfied Customers: 12549
Experience:  28 years experience, Master Mechanic
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I twisted a bolt off that attaches my thermostat housing to

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I twisted a bolt off that attaches my thermostat housing to my cast iron block. It's broken off below the gasket surface. I successfully drilled a hole in the center of the bolt and then managed to break an easyout off in the bolt. It was a bad day.

My drill bits are no match for the easyout steel.


There is not much you can do unless you have a high speed die grinder with a small bit to grind out that easyout. You may be best off to go to a repair shop to have them do it because even if you get it out you probably need heat to get the bolt out.

Customer: replied 5 years ago.

I have a high speed die grinder, air supply and a torch. Please tell me more about the bit to use and the technique. Thanks.

You will just need the smallest bit you can get that has grinding surface on all sides especially the tip so you can grind that easyout right out of the hole. I just work on the edges and grind towards the center of the easy out the vibration will often loosen the easy out and it will come out before you have to grind it completely out. Then I would heat the bolt and cool it really quickly with water maybe repeat that 3-4 times then a easyout will probably take it right out.
Customer: replied 5 years ago.

If I heat the bolt, won't I be heating the cast iron block too and then cooling it quickly possibly crack it or are my concerns unfounded?

You will want to concentrate on getting the bolt hot but the cast will get hot too but not as hot and I have not seen these crack but there is always a possibility, but there is not much else you can do if the bolt will not come out. If you really do not want to take a chance you will need to drill the hole larger and try tapping it out, this also could go wrong if the hole is not perfectly centered.
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Customer: replied 5 years ago.

Ok, keep your fingers crossed for me, and I'll let you know how it turns out.



Ok good luck
Customer: replied 5 years ago.

I saw a suggestion in a forum about welding a nut to the broken bolt. The bolt and extractor are broken below the surface. How would I weld to the bolt in that situation, and what do you think of the idea in general?

It is a possibility, I also do this if possible. You would need a mig welder and weld in the center of the bolt, build that up a little and then a nut can be welded to the top. After welding cool it down as I said before and try turning it out, if it will not come try heating and cooling again. You may need to weld a nut on more than 1 time they can easily break off the weld you built up. I usually do this on manifold studs and broken bolts in the head but it would also work in this case if you can get that built up so a nut can be welded on.
Customer: replied 5 years ago.

Any suggestion on preventing the nut from becoming welded to the top surface or internal threads while welding it to the bolt?

Not really you just need to stay in the center and weld, the weld does not like to stick to cast but it can if dirrectly welded to so just try to stay away from it.