Welch Plugs

What is the purpose of Welch Plugs in a water-cooled engine? Learn More
Welch Plugs are there to seal the openings created in engine blocks and cylinder heads to remove the sand used to create the coolant cavities during the casting process.
When the casting process is complete the holes left behind to remove the sand have no other purpose except maybe to flush the coolant cavities many years later during engine rebuilds.
These openings have to be sealed to contain the coolant in an engine block or cylinder head hence the Welch plug, it is usually press-fitted or screwed into the block or head to create a seal where-from coolant cannot leak out.

The most common Welch Plug found is the press-fit type.

On rare occasions, a screw-in type Welch Plug is used.

Welch Plugs are usually made of normal steel, copper or aluminium but are all similar in design and purpose.
Welch plugs tend to leak over time due to rusting from the inside when there is no antifreeze present in the engine coolant which prevent rusting.
It is therefore important to have antifreeze in your cooling system to prevent this unnecessary expense.

So when you experience coolant loss in your vehicle it may just be the Welch Plugs.

Replacing Welch Plugs

The process of replacing Welch plugs is sometimes complicated by its location on the engine block or head.

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