[Barnsnake]

As a marine service manager in a former life I have replaced literally hundreds of freeze cracked blocks and heads. I'll pass along lessons learned by my crying and wailing customers.

Shop heaters, light bulbs, and space heaters are great until there's an ice storm and the power goes out for days. Additionally, light bulbs burn out or breakers trip at the worst moments.

Those "Freeze plugs" are casting core plugs. I expect they were mis-named when they fell out after a block cracked. Sometimes they're still nicely seated in a chunk of cast iron on the floor.

NEVER ignore Murphy's Law. If there's a freezable liquid that resides in a location that could freeze under a bizarre combination of circumstances, it's in peril.