2000 Chevrolet Blazer - Cylinder Head Plug

What are Expansion Plugs?

Expansion plugs, also known as freeze plugs and cylinder head plugs, are located in several places around the engine block and cylinder head. 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. Expansion plugs are often made of brass or steel, and steel expansion plugs can corrode and eventually cause coolant leaks. If you notice coolant leaks around the cylinder head plugs, or the expansion plugs in the side of the block, you may need a replacement plug. In some cases, these plugs can also be made of rubber to seal oil channels, and may be designed to use a compression bolt and nut to expand the rubber plug to fill the hole and prevent leaks. If you notice oil or coolant leaks, or if you are rebuilding an engine, it may be a good idea to inspect and replace the freeze or expansion plugs to ensure continued leak-free operation. O'Reilly Auto Parts carries freeze plugs for most vehicles, as well as gasket kits, sealant, and more to help you make a complete repair.