One option available to you if your car's radiator is leaking, is the use of silver solder to repair the hole. Silver solder is a type of heavy-duty solder used to repair different types of metal. The use of silver solder, however, can be tricky because it will not bind to grimy or oily surfaces. As a result, the surface of your radiator will have to be cleaned thoroughly. Also, silver solder will not adhere to wet surfaces either, so it will be absolutely necessary for you to make sure your radiator is drained and completely dried before you attempt the repair.
Locate and mark the spot where your radiator is leaking. You can do this by filling it with water and simply spot-checking to pinpoint the leak. Once the leak is found, empty the water from the radiator and mark the area to be soldered with tape.
Dry and clean the area around the leak thoroughly. As mentioned, silver solder will not adhere to greasy, oily or wet surfaces. You can use a wire brush to scrub away excess grime and gunk. You also want the radiator as dry as possible. Use a blow dryer to dry it off thoroughly, if necessary.
Sand the area where the hole is using silicone carbide sandpaper, which is a special type of sandpaper used on metals. The goal here is to remove paint or rust if there is any present on the radiator where you intend to make the solder repair.
Heat up the soldering iron. A powerful soldering iron is needed to melt silver solder. You will need at least a 400-watt soldering iron.
Apply the flux to the area where you are going to solder the leak. The flux will eliminate oxidation, thus making the solder bond more solidly.
Touch the soldering iron to the flux until it turns light brown in color.
Remove the soldering iron quickly and place the silver solder against the area. The solder should melt evenly across the area where the leak is. Allow the radiator to remain dry over night.
Fill it with water to make sure the solder bond is holding water.
