If your radiator is damaged and the damage is not too intense, it may be possible to repair it yourself using solder and a soldering iron. Unlike brazing and welding, soldering is not a process that physically bonds one piece of metal to another. Instead, it can be thought of like a patch made of metal. Like welding, more solder does not always mean a better soldering job. As long as it is accomplished with some care, the repair cold last the car’s lifetime.
Start by preparing the damaged area for solder. In order to do this, use a wire brush or a small grinding wheel to remove any paint in the area. Any sharp edges should be removed as well. If not used correctly, a grinding wheel can make the damage worse, so be careful with it. Radiators are composed of very soft metals. Use a strong cleaning solvent like Brake Cleaner or Simple Green to clean the are that you will be soldering. This is so that the solder adheres directly the the metal, not to particles of dirt and grime lying on the surface of the metal. Check for other damaged areas before proceeding.
Use solder and a soldering iron to cover the area completely. A high wattage soldering iron should be used, and the solder wire itself should be very thick as well. Make sure that the iron is completely heated before you begin in order to ensure that the solder melts completely, allowing it to adhere to the damaged part of the radiator much more effectively. The damaged area of the radiator should be heated thoroughly with the iron as the wire is fed into the damaged area very slowly. Be careful not to drip bits of solder into the interior of the radiator itself. Add solder to the edge of the damaged area, circulating around the crack until the ends of the solder meet. Be sure to unplug the soldering iron when you are finished. Most soldering irons do not have and off switch.
Use a small grinding wheel or wire brush to eliminate any sharp edges or burrs created during the soldering process. This ensures that the solder line is as smooth as possible and that it does not contain any foreign materials that can wear down at it over time. If you choose to, you can repaint the soldered area, although this step is not strictly necessary. Finally, fill the radiator up with radiator fluid and start your car. Let the car get up to full temperature and watch the soldered area in order to ensure that there are not any leaks.