[Simple Man]

Originally Posted by Fullsize455

That's because they aren't freeze plugs, they are core plugs for evacuating sand out of the block during the casting process. They have nothing to do with freezing, despite the myth that has been perpetuated for decades.

https://en.m.wikipedia.org/wiki/Core_plug

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

[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.

[Simple Man]

Originally Posted by mgarblik

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.

I wouldn't have thought so, thanks for clearing that up!

[Fullsize455]

Originally Posted by mgarblik

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.

Same, I've seen and heard of many engine blocks and heads cracking due to freezing, but I've never once seen a core plug pop out due to freezing. Even if it did, it would be way too late.

[Heybuck]

A little bit off topic but I've seen a small freeze plug blow out under pressure in the cooling system.

My sister-in-law had a 1984 Nissan Bluebird. Appalling car - look it up. 4 cylinder 2 litre engine. She called me to say the engine had run out of power driving on the freeway. And it "smelt funny". So I go and fetch her and see the engine has been red hot and the sump is full of soupy white oil.

Towed it home and had to pull the engine. Engine had been replaced a few of years earlier but it was long out of warranty. Cheapo job done. Those engines are a cast iron block, aluminium head, overhead cam, and the entire timing chain/water pump housing is also alloy. In the front of the engine between the block and the timing cover is a 14mm freeze plug. It was OLD. Had not been replaced when whoever had gone through the engine. And it blew out, straight into the timing chain housing, dumped in the water and that was then end of the thing.

Guess who had to go and find a good second hand engine, replace ALL the freeze plugs and get the thing going again.

[Firedup6975]

You might copy and paste this post in the members helping members forum as well.