Did you ever listened this term?? Though it’s not a quiet used term we must know what it is. So we will start with what’s a freeze plug??
If you have a look at the side of an engine block you will see a line of circular holes about an inch and a half in Dia and about a quarter of an inch deep. Actually these are the holes in the side of the engine block which are plugged with a dish shaped metal plug called a freeze plug or expansion plug.
These freeze plug also called with the names of expansion plugs, core plugs, frost plugs and Welch plugs.
When it comes to play is if you run just water with no antifreeze in your car’s cooling system then the water can freeze. When water freezes it expands. If water freezes inside your engine block, it can expand and crack the block. Freeze plug will pop out, relieving pressure and saving the engine block from cracking. ( Although most times engine cracks anyway ).
But in reality this doesn’t work all the time because many blocks get destroyed by cracking without the freeze plugs popping out, or if they do pop out the block cracks anyway.
Antifreeze has certain properties that can cause freeze plug to rust. Rusting of freeze plug will lead to cracks of the plug which results in leaking of coolant. So it’s well recommended for frequent checking of freeze plug.