Well, pulling off the thermostat and when I got to the bolt, the head broke off. I did remove the thermostat and the bolt still protrudes. What is the best way to remove this? IMG_3859 by mhdriver posted Jan 14, 2026 at 2:12 PM
I'd carefully heat up the thermostat housing with a torch and use a vise grips to grab whats left of the bolt to remove it. If that doesn't work you can try to drill it out for using an extractor or drill it all out and helicoil.
Please don't start a new thread for the same subject. Post it in the original postings.... Heating it up to loosen it is the best way. Lot's of penetrating oil, and let it soak. You "might" be able to twist it out with vice grips. If not, you can drill a hole in the middle and hopefully and easy out will work. If not, drill it out and tap new threads.
Will post anything else in original thread. Got to say this is discouraging since it's not in the open. Getting penetrating oil and a torch today.
Yes, it can be a pain. Try to stay calm, and be don't go fast. Do one thing at a time. It's tricky, but it can be done...
Where drilling it is difficult is that there's no way to get a drill down there that I can see. People say extractors rarely work if at all. I'm gong to heat it and then use penetrating oil to see if I can get it with vise grips.
Would you replace all the engine cooling hoses? 2015 with 205k miles. No apparent leak, but I seem to be losing a minute amount of coolant every 6 months.
Could you post a link to that thread; is it one you started? I looked in vain. Was there discussion of head gasket failure, in the other thread?
I think he was referring to my post about figuring out the parts. For what it's worth, I tested the coolant, no exhaust fumes per the test solution. So I feel pretty comfortable about the head gasket. That's such a big job that I'm not going to do it until I have to, if I have to ever do it.
Knipex pliers please . They cheap now days . Worth it . Kroil applied every few hours for a day . Then mapp gas yellow can. Out she comes barely grabbing w knipex
Two thin nuts like locking nuts for holding positions on various jigs and fixtures . But that's a stretch
I got pointed locking pliers, penetrating oil and a butane torch refill. Going to give a few rounds of oil first and see if I can take it out without heating it. The head of the bold twisted off easily, which may mean it will still come out fairly easily. Drinking my last cup of coffee before I return to the battle now .
As you say, that test is for exhaust in coolant, which is not the usual 3rd gen failure mode: it's usually coolant leaking into combustion chambers. If it drags on long enough unrepaired, then you may get exhaust in coolant as well. Anyway, this is all off-topic: since this thread is ostensibly about getting a broken bolt out.
There are right angle head you can put on a drill to get in there easier. Use the penetrating oil first, then hopefully the vice grips will work. No reason to replace the hoses unless they are damaged. Those tests don't work on the Prius. It's rare for the exhaust to leak into the coolant. You have to do a pressure test and a bore scope down the spark plug holes. With 205,000 miles it's possible you are close. But only small amounts of coolant over a long period of time is nothing to be too concerned with. Look carefully for other possible leaks though. It would be a good idea to check the pistons. If coolant is leaking, #1 and 2 are the likely ones. If you catch it early, you could save a warped head, and/or possible bent rod. You'll know if you start getting the knocking on a cold engine...
So far, no dice. put pentrating oil on it, heated it twice but i couldnt get the bolt to glow. my locking vise grips are a joke with this. I have obviously angered the gods in a prior lifetime.
Tom's quote edited for emphasis You have an advantage with part of the bolt exposed. Don't waste that advantage. There is skill involved so consider towing it to a quality shop and let them do it. Butane and propane are not hot enough. Mapp gas is hotter but you have to be careful to not overheat the aluminum around the bolt. Another high skill technique is to weld a nut on to the broken bolt. Kroil and Knipex
