Cylinder Head Plug

Expansion plugs, also known as freeze plugs, serve a dual purpose. When an engine block or cylinder head is cast, these ports are used to hold the internal passage molds that create the coolant and air channels as well as the cylinders of an engine. Freeze plugs are then installed to cover these holes, and also may help to keep the block from cracking in freezing temperatures. These plugs allow freezing coolant or water to expand without cracking the cylinder head or block. They are often made of brass or steel, and steel expansion plugs can corrode and cause coolant leaks. If you notice coolant leaks around the cylinder head plugs, or the expansion plugs in the side of the block, check out the options at O'Reilly Auto Parts. We carry freeze plugs for most engines.