Welded on a nut and it broke off flush with the aluminum. After an eternity of missteps, I got an insert installed. It's definitely able to handle torque and I've got it in with Red Locktite. It's not perfectly centered, have dremeled the thermostat housing a bit to make it work. That was a terrible spot for a broken bolt, but going to install the thermostat tomorrow, using a thin bead of grey Permatex around the perimeter. Only able to do this job by boroscope and fishing 3 flexible drill extensions through the engine, put little pieces of pvc pipe around anything that turned. It's easy to goober up your wiring with the drill extenions if you aren't careful. Should be back on the road by Wednesday . IMG_3892 by mhdriver posted Feb 8, 2026 at 3:57 PM
Thanks. I did speak to a well known hybrid shop about a head gasket and the guy straight up told me "We've never seen a bad Prius thermostat". I'm feeling like an idiot for ever touching it. On the bright side, it was a great education. I did price an engine swap in Orlando, pretty darn reasonable for a JDM, just $2000 plus tax. First sign of head gasket issues, that's what I'm going to do.
They have been known to go bad. But it's rare. And really doesn't hurt to replace them when they have a lot of miles on them. Usually, it's an easy replacement, but life happens. No one can really be certain if they are getting a real jdm engine. And how do you prove it have 50,000 miles or less on them? Either way, you are getting a used engine, they might have been sitting for months or years... You could start making plans and getting the parts together to replace the head gasket, before it fails...... A LOT less work, and cost...
