When repairing Honda radiators, don't use radiator adhesives and sealants because these merely provide a short-term solution to the problem. A Honda radiator can either be made of copper, aluminum or plastic, and different repair processes apply to each. Copper and aluminum variants can be welded or brazed, while modern plastic variants are irreparable in general, regardless of the size of the hole or leak.
To repair a copper or aluminum radiator, first clean the area of the leak, and remove any paint with a steel wire brush or portable grinder to expose the metal. This gives the solder enough bare metal to adhere to. Use a soldering iron that's 60 watts or more. Low-wattage irons do not have the power necessary to melt the soldering wire and heat the radiator metal properly
When soldering a metal radiator, start by heating the damaged area of the radiator, then the soldering wire. Press the soldering iron to the radiator surface until it is hot enough to accept the melted soldering wire easily. Solder the melted wire onto the radiator slowly, making sure to cover the entire crack or hole. Once the leak or hole is completely covered, grind the solder to a smooth surface.