What is a core plug?

What is a core plug?

A core plug is a thin piece of metal either in a cup or dish shape. It is used to block off a opening on an engine block or cylinder head. Most common types of openings can be coolant castings. Or drilled oil galleries within the engine.

Other common names for core plug are welch plug, freeze plug and expansion plug.

Core plugs are fitted to nearly all diesel and petrol automotive, marine and industrial engines.

Materials used to produce the plugs are usually mild steel with zinc plating. Stainless steel, brass and aluminium can also be used.

Mild steel core plugs as the most common, they are usually finished with a zinc-nickel electroplating finish to form a corrosion resistance against fluids and high temperatures once fitted to the engine or cylinder head.

It is common practice when rebuilding or overhauling an engine block or cylinder head to remove all core plugs to clean the all the coolant and oil gallery areas thoroughly especially if the engine block or cylinder head have been soda or shot blasted. All the core plugs are replaced when it is being built back up.