Description
Freeze plugs, also known as core or expansion plugs, are small but critical components pressed into the engine block. Despite the name, they aren’t designed solely to protect against freeze damage. Their primary role is to seal the holes left behind during engine block casting, keeping the cooling system closed and pressurized.
Because they’re constantly exposed to coolant, poor maintenance can lead to corrosion, rust, or electrolysis, eventually causing leaks. A failed freeze plug often shows up as coolant dripping from the side or rear of the engine—and rear plugs can require major labor to replace.
Typically made from steel or brass, brass plugs are favored for their corrosion resistance, while rubber plugs are sometimes used for temporary repairs. Simple in design but vital in function, freeze plugs quietly protect your engine until they don’t.