Core plugs sit in different places around your car’s cylinder head and engine block. Their main purpose is to seal holes cast in the engine block or head as part of the manufacturing process. They also help prevent the engine block or head cracking in the event that your coolant freezes. If you find leaks around these places, your core plugs may be worn and need replacing. Core plugs suffer from corrosion and may pop out when put under pressure by expanding ice. When subject to excessive wear, core plugs can blow out completely. This will result in a sudden loss of coolant. This fluid can then make its way slowly through rust holes or around the edges of your engine. This will normally leave a stain on the