Expanding core plugs are a temporary fix.

 

That happens, some sort of fiddle factor, I reckon. Over the years I've pressure test lord-knows-how-many systems and sometimes a leak just doesn't present itself....but I know darn well that it's there somewhere !


cheers
DD

 

My first car, an Ancient Chrysler, which I bought for a college shop project, had all the plugs removed and the block and heads boiled. (In Montana that could be done)

When I put the plugs back, I didn't get one in the right head seated properly, and the first time it got good and warm (out on the open road of course, 10 miles from town) there was a 'tink' sound and an Enormous cloud of steam billowing from under the hood, followed immediately by the needle pegged on H.

I shut it down, coasted to a stop, got a tow back to town, and replaced the plug with exactly what Carl describes; a rubber plug with a squeeze nut so I didn't have to pull the engine to fix it. It stayed that way as long as I had the car and never gave a moment's trouble, nor did any of the other plugs.

Lesson learned, and I've not made that mistake again.
(';')