[mgarblik]

Originally Posted by Simple Man

Correct, but they are made out of thin metal, instead of heavy cast iron, so they usually go first.

That has not been my experience in over 45 years working with engines. The softer, flexible core plugs just sit there nice as can be in the block and heads and the brittle cast iron cracks all around the plugs and elsewhere, then the plugs might fall out. Only exception I have seen is if the plugs are extremely rusty already or incorrectly installed. Then they might push out if the engine is frozen. As mentioned, they exist to remove casting sand. Many newer engine castings don't have them, if foam cores are used. Just went through a similar experience with a friends Sea Ray only a 4-cylinder. Cracked the block and head. He sold the boat for $900.00. It was going to cost more than the boat was worth to fix.