Radiator stop leak is a common additive that is designed to seal minor leaks in your radiator and leaks in-between components. While itÒ€ℒs an aftermarket additive, some car manufacturers use it on new Ò€¦ Irontite ceramic motor seal - engine cooling system sealer for head gaskets, radiators, leaks, & cracks - prevents corrosion & rust, improves cooling performance, stops overheating & coolant Ò€¦