That's not good....

So I started in on replacing the water pump on my miata tonight. Figured since I was putting in a new thermostat while I was there I would take the top half of the housing off and get that part out of the way while I was pulling hoses and intake piping and belts and the radiator and .... you get the idea. Well apparently it has been a LOOOOONG time since the thermostat was changed out, as both bolt heads snapped off. After the first one, I sprayed down the second with pb blaster, let it sit for a bit, sprayed it again, and bumped it back and forth a few times before trying to get it out. No joy, it broke as well. So my question is, do I take a grinder to em, knock off as much as I can without digging into aluminum and attempt to drill em out, or keep hosing them down with penetrating fluid, and try vice gripping them out? does the lower half of that housing come off the block?

Find a nut that just fits over what's left of the bolt and drop it on.

Now weld the nut to the bolt stub. The heat will help break it loose.

Wrench the damn thing out.

In the future, if you've got steel parts stuck in aluminum, heat is your best friend.

Warm the casting up until it starts to steam a bit, a quick shot of your favourite penetrating oil and get a wrench on it.

Shawn

I'd do just about anything to avoid drilling it. Save that for the last resort. Drilling steel out of aluminum sucks.

I would give Trans-Maro's idea a try. The combination of heat and a new head will probably pop it right out.

The lower housing does bolt to the block, but not sure what else needs to come off. I think if you're doing waterpump you'll be able to get to it fine.

Yup, heat is your best friend here. Transmaro hit it. If you can do that, try. Drilling is fraught with potential disaster.