Core plug

[old_master]

Core plugs, sometimes mistakenly referred to as "freeze plugs”, carry a myth that they will "pop out" if an engine block freezes. The fact of the matter is that they usually rust out as a result of cooling system neglect. They’re installed at the factory with a glue or sealer on them to prevent leaking, which also makes it difficult for them to “pop out”. If you’ve ever had the pleasure of replacing one, you know what I’m talking about. The reason they are there? When an engine block is sand cast, (made) sand is poured into the mold. After the block has cooled, holes are drilled in the block, one near each cylinder, and the sand is removed leaving a void called, you guessed it, a coolant passage, or water jacket.

[rlith]

Originally Posted by old_master

Core plugs, sometimes mistakenly referred to as "freeze plugs”, carry a myth that they will "pop out" if an engine block freezes. The fact of the matter is that they usually rust out as a result of cooling system neglect. They’re installed at the factory with a glue or sealer on them to prevent leaking, which also makes it difficult for them to “pop out”. If you’ve ever had the pleasure of replacing one, you know what I’m talking about. The reason they are there? When an engine block is sand cast, (made) sand is poured into the mold. After the block has cooled, holes are drilled in the block, one near each cylinder, and the sand is removed leaving a void called, you guessed it, a coolant passage, or water jacket.

Yeah, pretty common knowledge, but thanks for the reminder on the topic. The problem is as well that they use aluminum freeze plugs. The reaction to these 2 metals (iron and aluminum) over long periods of time isn't good. (Generally 2 differing metals will eventually corrode when in contact with eachother). One of the best things to do though is try to limit that corrosion. Install brass freeze plugs and you will get much more life out of those than you will aluminum replacements.