Your car is overheating, and you don't have the cash for anti-freeze. You fill up the radiator with water, and you forget about it. If you live in a cold climate, during the winter the water inside your engine block can freeze. Freezing water can crack an engine block, requiring complete engine replacement. This tends to get rather expensive, so the manufacturers have built in a system which may prevent your block from cracking.

There are several places where the manufacturers have placed holes through the block to the water jacket, which is the area where water circulates to cool the engine. Instead of plugging this hole with iron, they use a softer metal like brass. Should the water jacket freeze, if enough pressure is present to crack the block, the freeze plugs are supposed to pop out, saving the engine from irreparable harm. The holes where the freeze plugs were allows the expanding ice to escape.

Whenever an engine is rebuilt, you should always replace the freeze plugs. They're cheap safety items in case you get stuck in a cold climate.

machfive says: Dude. Freeze plug is nice - BUT - You should add, "It's always nice to carry a jug of 50/50 water/anti-freeze in your trunk. You WILL need it, someday, if not for you, then to be a good samaritan to someone else.

stupot says: It might be worth mentioning that not buying antifreeze is truly false economy... saving a few pounds/bucks/euros now only to have your engine ruined in a few months! My A-series engines don't have freeze plugs, so I wasn't aware of them.

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