CRC K&W Block Seal Permanent Metallic 16 oz – Engine & Radiator Leak Repair, Metal‑strength Bond

CRC K&W 401016 Block Seal Permanent Metallic™ is a professional-grade 16 oz coolant system sealer that forms a metal-strength molecular bond to permanently seal cracks, holes and leaks in engine blocks, heads, radiators and heater cores.

This concentrated formula was developed to repair cooling-system breaches in both gasoline and diesel engines without welding or part replacement in many cases. Independently lab-tested and designed to resist flow and breakdown under high temperature and pressure, it works on cast iron and aluminum blocks as well as copper, aluminum and bi-material radiators. Use it as a fast, shop-quality repair option when a temporary stopgap won’t do.

How does this product repair a cracked engine block or head gasket?

The sealant creates a durable, molecular-level bond that locks into metal surfaces, filling and reinforcing damaged areas rather than just coating them. It hardens into a metallic-like seal that resists coolant flow and pressure, helping to stop active leaks.

• Forms a permanent molecular bond that mimics steel-strength adhesion
• Pours into and fills cracks, cavities and gasket breaches
• Works on both cast iron and aluminum engine components

Will it hold up under high temperatures and coolant flow?

Yes — the formula is engineered to withstand the extreme heat, pressure and continuous coolant circulation found in modern engines. It’s designed not to break down or wash away once cured, making it suitable for long-term service.

• Stable under high temperature and pressure conditions
• Resists dissolution in circulating coolant
• Meets professional standards for durability in cooling systems

Which vehicle systems and materials are compatible with this sealant?

It’s formulated for broad compatibility across water-cooled systems. Use it on engine blocks, head gaskets, freeze plugs, radiators and heater cores made from common automotive metals and bi-material constructions.

• Effective on cast iron and aluminum engine blocks
• Seals copper, aluminum and mixed-material radiators and heater cores
• Suitable for both diesel and gasoline cooling systems

How is the product applied and what should I expect after treatment?

Application is straightforward: add the recommended amount to the coolant reservoir or radiator per the instructions, run the engine to circulate, and allow the formula to locate and seal leaks. Results can be immediate for small leaks; stubborn or large damage may require repeated treatments or complementary repairs.

• Pour measured dose into coolant system as directed
• Run engine to circulate sealant to leakage points
• Inspect and, if necessary, repeat or follow up with mechanical repair

Who is this for: CRC K&W 401016 Permanent Metallic™ Block & Radiator Seal is aimed at professional technicians, fleet maintenance shops and experienced DIYers who need a high-strength, lab-tested sealing solution for cooling-system leaks. It’s ideal when welding, part replacement or teardown are impractical, when downtime must be minimized, or when a lasting repair is preferred over temporary additives.