What is the purpose of frost plugs or core plugs in engine blocks?

Frost plugs, also known as core plugs, play a crucial role in the engine manufacturing process, specifically regarding the removal of sand or debris used in the casting process. When an engine block is cast, sand is often used to create the hollow spaces necessary for coolant passages and cylinder bores. After the casting is completed, frost plugs are inserted in the holes where the sand was located to ensure a clean finished product. This helps to prevent any residual materials from obstructing the coolant flow, which is essential for the engine’s cooling system.

While frost plugs do have other functions, such as allowing for expansion of coolant to prevent freezing in cold weather (which leads to the term "frost plug"), their primary initial purpose is related to facilitating the cleaning out of sand from the casting process. This prevents contamination and ensures optimal performance of the engine by allowing proper circulation of coolant.