A radiator sealant, also known as radiator leak sealant, stop-leak, or coolant leak sealer, can provide a quick fix for leaks. Coolant sealant leak repair can fix the leaks inside a radiator by sealing the pores of the radiator and plugging the point from where you're leaking coolant. When used correctly, it can effectively seal mild leaks in the cooling system of a car. Additionally, leaks stemming from the head gasket, engine block, or water pump can be fixed with a sealant.