I was tightening a bolt a few weeks ago to see if it would stop a leak and it made a loud pop and moved 1/4 a turn. Bolts still tight, bolts not stripped I didn’t try tightening it anymore after that. It was on the T-stat housing, I didn’t take it off and still haven’t. I’m taking it apart tomorrow.

 

Not positive, but it sounds like over torquing put the casting under pressure until it fractured.

 

agreed.
sound like the T-stat housing cracked

 

Alright, kinda figured. Not a big deal I was just worried of the possibility of the intake manifold side being cracked or something. I’m taking it off soon.

 

I'd bet the thermostat wasn't in the recessed area and that caused the housing to snap when bolt torque was applied.

 

Nothing was cracked not the housing or the intake manifold. The bolt was bottoming out though

 

Maybe the bolt broke through to the water jacket in the intake manifold.
If that is the case you will need to seal the threads on the bolt.
Pretty sure 351 is a blind hole but 302 is open to water jacket.
Not sure what you are working on.

 

302, I just ran it nothing came out by the bolt, it didn’t build pressure. But no leak. I gotta cool it off and start it again with the cap on.

 

Could be a 12 point socket "slipping" on the head of the bolt.
Were you using a 6 point socket ?

 

I have an early truck EFI 5.0 lower & a couple Mustang & Explorer manifolds. All blind holes.

 

It was a 12pt it was a wrench with a 90 degree bend to fit where the bolt can’t fit a socket on it without taking anything else apart because the ac mount stuff. I didn’t even think about that.

 

Something happened when the bolt made the noise. You are lucky the bolt didn't break off in the intake manifold. I suspect the threads in the hole may be stripped and you should check that by re threading the bolt (not to tight) now and make sure it has not stripped or is loose in the hole. You can visually check the bolt threads before you do that. If they are messed up replace that bolt. Final torque on the bolts for the housing are ONLY 12-18 ft lbs. That isn't much and is easier to achieve with an inch torque wrench. If you do it by hand just snug them to firm and if it leaks you can always go a little more. You don't want to break the bolt in there, ask me how I know.

 

I replaced the housing and it came with new bolts, and they threaded in fine. I bet it was the wrench slipping.

 

That's good to hear.