CRC 5371 Copper Block Weld Permanent Block & Radiator Sealer, 16 Fl Oz Go to amazon.com Related posts Top recommendation for gasket sealer engine FeatureBlock and Radiator SealerModified liquid glass formulaNot VOC Compliant for California & OTCPermanent block and radiator sealer DescriptionThe Copper Block Weld permanently repairs cracks in iron and aluminum heads, radiators and freeze plugs using a copper ceramic sealing system.