Broken bolt - thermostat housing

[LShute]

I have to replace my thermostat (90 diesel), and it sure feels like I'm going to snap two of the bolts off that hold the housing to the head. I've been thinking about this for several days, planning to put a torch on the head as close as I can to where the bolts go in, and try heat. But lots of bad visions dance in my head. Cracked head, warped head, ruined gasket since the head will be getting real hot but not the block. I'm wondering if it might be best to just let the bolts twist off, if that's what they do, then try to drill them out. I've got some PB Blaster (heard about it by searching this site), but I can't get it anywhere near where it needs to be unless the housing is off. If I twist the bolts off, what next? Thought I'd soak the holes, or stubbs if any are sticking out, with PB Blaster, then try reverse drills and hope I can drill the bolts without screwing up the female threads. If I do screw up the threads, drill them out a little bigger, tap for a larger bolt and go that route. But, the problem now is whether to use heat on the head. The more I think about it the worse that idea seems. Thanks for any help.



Larry

 

[DavidC]

Personally I would try the heat method first instead of just turning until they broke. Warm them up real good and if you can tap them with a hammer (after warmed up). At least that way if they do snap at least you tried. There is quite a bit of metal there to help dissipate the heat just do not try to melt it.



Dave

 

[Paychk]

I learned some tricks a long time ago and a real big NO-NO in regards to cast iron.



NEVER EVER heat cast iron if at all possible, 99. 9% of the time it will end up cracking. I would try the PB Blaster and vibration to work it into the bolt head/shank. When you think it is ready, alternate the turning force loosen/tighten the bolt will help immensely. As a last resort, if the bolts break off, drill down the center of the bolts and use an oxy/fuel torch (oxidizing flame) to heat just the center of the bolt shank(Keep the heat away from the cast as much as possible), let cool and they will back right out with little or no effort. Another thing you can do when the bolt shanks are hot, rub a candle at the junction of the bolt shank/threaded hole, this will provide some lube to the threads.



Good luck!

 

[JLEONARD]

I agree not to use heat... . if the PB and the tapping don't work and the bolts break you can always drill them out.

But we all hope it doesn't come to that.

Good luck.

Jay

 

[LShute]

Thanks for the suggestions so far. Another thing that I've thought about is drilling into the head where the bolt threads are, and probably just a little into the bolt, but trying to stop just at the bolt. Then squirting some PB in that hole over 2-3 days. This would deliver the goods to where they're needed (good), but weaken the bolt some, assuming I'll go into the bolt a little (bad). The bolts that are stuck are the two near the front, so I can probably get a small drill in there. I've never used the PB Blaster before so don't know how well this stuff works. My experience with Liquid Wrench is limited but I don't remember any real successes, so I'm hoping the PB Blaster is way better.



Larry

 

[Philip]

PBlaster is better than Liquid Wrench.

 

[Paychk]

I've turned wrenches for over 30 years, it is the best that I have seen. Remember to tap on the bolt right after you apply it, while it is still fluid around the bolt or nut. A brass punch and hammer, up to a air chisel with a blunt end really makes this stuff work!