I'm still baffled as to why. I've never even heard of blowing a freeze plug....

 

This is why, I call him the come back kid.
If his truck goes down he's right back up in no time leaving a trail of dust
racing down the desert roads.
Orich

 

I think it was a combination of things. Specs and dimensions of that particular plug being the 1st. The aftermarket world not as picky as Ford. A few thousands shy can start it. Remember Brass is a soft metal. So it's "friction fit" won't be as tight.

 

other things
was paint removed from holes before installing freeze plugs
if cold out and engine cold freeze plug could have shrunk a little
after market water pump put out more pressure
or just POS made in china freeze plugs

 

I always freeze my freeze plugs for 2 days before installing then put a light coat of J/B weld on contact surface (steve christ book tip)

 

The blown freeze plugs while cranking had me scratching my head. But there is a possibility:
Not water pressure. The radiator cap will blow off at 14psi. But block strain is a possibility.
All the horse-pressure you put on the rear wheels while cranking is a result of cylinder pressure which tries to blow the heads off. If the freeze plugs were marginal the pulling of the heads and twist on motor mounts could have made the pop.
That is my best guess but like so many oddball problems here, only God knows.
Glad that you fixed the problem and caught it early.

 

You might be onto something there John, that's the best explanation I've heard anyway

 

Look at the thickness of the land (surface) where the plug rests. Is it thin?

 

No, it's normal thickness. 3/16" or whatever.

 

truck gets up and goes pretty good for having 3.25 gears and an AOD im glad you have figured the problem out good luck and i hope the best for you and your truck

 

I have always wondered why some of the hot engines- like the Boss 302- have screw-in freeze plugs. Maybe the guy who can answer that question can tell us why your freeze plug blew.

 

Boss 302s and other performance engines were available in production cars for motorsport homologation purposes. The screw in freeze plugs were designed to keep fluids off of the racing surface.
IMO, the freeze plug popped out either because the plug itself was of poor quality (sizing or material) or was not properly installed.

 

It's holding. I haven't revved way up again yet however.

 

Factory 4bbl 351 Clevelands with auto trans shifted at 6,000, WOT.

 

Well shoot....