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Saturday, July 15, 2006

 

Freeze plugs aren't for freezes

It's time for another episode of Mechanical Mythology! Here, we deal with the pressed-in plugs on the side of an engine block. They're about 2" in diameter, and most people don't have to deal with them unless they start leaking. They are popularly known as freeze plugs, but this is something of a misnomer.

Claim: Freeze plugs in an engine block are there to protect the block from the coolant freezing.

Status: False.

It seems logical that freeze plugs are meant to guard against ice. They are simply pressed in, so too much pressure behind them will press them right back out. So it seems this could save you from a cracked engine block if you didn't put in enough antifreeze.

Actually, that's not what they are there for, and the manufacturers don't even call them freeze plugs. The term they use is core plugs. And the holes they occupy are not there for any reason other than making the engine easier to manufacture.

The holes in the block are not for ice, but for sand. All cast iron blocks, and some cast aluminum ones, are made by sand casting. The mold is a mixture of sand and clay. Cores are special pieces of the mold that fill hollow scections of the metal, such as the water jacket around the cylinders. A system of pins reaches in through holes in the block to support the cores. After casting the block, the core breaks up, and workers remove the sand from the core out the same holes. Then they cap the holes with the core plugs.

And that is the entire reason for the core plugs. Unless you want to put a block heater in one.

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