J-B Weld radiator repair kit 2120 — 3/8" hole & 4" crack patch, epoxy putty with fibreglass cloth

This kit combines epoxy putty, fiberglass cloth, sandpaper and an applicator to create a durable, heat-resistant patch for holes, cracks and weeps in radiators, washer reservoirs and other fluid-containing components. It’s formulated to bond to plastics, composites and metals commonly found in cooling systems so you can perform repairs on-vehicle or on-bench with straightforward steps.

How does the kit stop radiator leaks without removing the tank?

The repair system cures into a hard, adhesion-focused patch that fills gaps and reinforces the damaged area. Applied directly over the leak after surface prep, the fiberglass and epoxy combination conforms to irregular shapes and creates a seal that resists coolant and vibration.

• Epoxy putty molds to shape and hardens to form a solid repair.
• Fiberglass cloth adds tensile strength and crack resistance.
• Sandpaper ensures a roughened surface for better adhesion.
• Applicator helps seat the patch and remove excess material.

What size damage can the J-B Weld 2120 kit handle?

This kit is designed for small- to medium-sized repairs: it fills holes up to about 3/8" diameter and stabilizes cracks up to approximately 4" long when applied per instructions. Larger or structural failures may require part replacement or professional service.

• Ideal for pinholes, small punctures and hairline cracks.
• Effective for washer fluid tanks, overflow reservoirs and radiator tanks.
• Not intended as a permanent fix for severely crushed or corroded cores.
• Works on both plastic tanks and many metal surfaces when prepped.

How long does the repair take and what environmental conditions matter?

Curing time varies with temperature and humidity; the epoxy typically sets to handle light pressure in a few hours and reaches stronger cure over 24–48 hours. For best results, clean and dry the repair area thoroughly and avoid extreme cold or wet conditions during initial cure.

• Surface must be clean, dry and roughened with included sandpaper.
• Allow initial set time before subjecting the repair to coolant pressure.
• Warm, dry conditions accelerate cure; cold slows it down.
• Follow the included instructions for mixing and layering the fiberglass.

Can this kit be used on other parts besides radiators?

Yes—the components bond to a wide range of materials, making the kit useful for washer tanks, water storage containers, PVC, composites and some plastics. It’s a handy multipurpose repair pack for motorcycles, ATVs, small engines and household tanks where a routed patch is acceptable.

• Compatible with many plastics, composites and common metals.
• Useful for automotive, marine and light-farm repairs.
• Not a substitute for replacing parts in high-pressure industrial systems.
• Always test adhesion on an inconspicuous area if unsure of substrate.

Who is this for: The J-B Weld 2120 Radiator Repair Kit is tailored for DIY mechanics, home enthusiasts and professional technicians who need a practical, on-vehicle solution for small radiator and plastic tank leaks. If you want a portable kit that provides reinforced patches for common cooling-system damage without immediate replacement, this product gives the tools and materials to perform reliable, long-lasting repairs when used as directed.