Radiator leaks just happen. According to the National Automotive Radiator Repair Association (NASRA), actual age has more to do with radiator leaks than mileage. Over the years, your car is exposed to numerous environmental factors - such as road salts, debris, and various chemical reactions that can cause the metal in the radiator core to break down leading to radiator leaks and the need for radiator repair.
The most obvious sign of a radiator leak is of course a low coolant level. It's a good idea to inspect this visually from time to time to avoid a major radiator repair scenerio. Since low coolant levels can cause additional damage in a pressurized system, you should make sure this is topped up as needed. Another sign of a radiator leak is a puddle under your car. This puddle will appear as a bright, neon-green liquid with a vaguely radioactive look to it, as well as a slimy feel. This is ethylene glycol, or anti-freeze that comes out during a radiator leak. It is EXTREMELY toxic, so make sure this gets cleaned up and disposed of properly.
Once you've determined that you have a radiator leak, the next step in your radiator repair is to identify the location of the leak. The best way to do this is to wash the radiator and hoses with water, then start the engine and examine the system for signs of a radiator leak. There's a good chance that your radiator leak may actually be in one of your hoses, which is a relatively easy radiator repair to fix.
If it turns out that the radiator itself is the source of the radiator leak, it may be possible to patch it - at least temporarily - with a ""cold weld"" epoxy such as J-B Weld. The problem with commercial radiator ""sealants"" is that they impede the flow of water in the radiator core and abrade the water pump seals - but never actually seal the radiator leak. Once you have identified the source of the radiator leak - usually on a seam - drain the radiator, clean the area around the leak thoroughly, then apply the J-B Weld. Before refilling the radiator, move the overflow line over to a vacuum port on the intake manifold, then remove the distributor cap and crank the engine a few times. The vacuum will pull the JB-Weld into the cracked seam, making a better seal to prevent the radiator leak.
If you determine that the radiator leak culprit is a broken radiator tube, you'll need to dig the cooling fins away from the tubing with pliers. Next, cut the tubing and wrap the cut ends up on themselves (like a tube of toothpaste). Crimp each end tightly, then apply JB-Weld.
Once repairs are affected, it will take about two hours for the JB-Weld to fully cure. It's also desirable to use a lower pressure cap (about 7-9 lbs psi). Remember that this is a temporary radiator leak fix. Ultimately, your radiator leak will require the attention of a professional. In the worst case scenario, you'll need a new radiator - in which case, Radiator.com is here to ease your pain with discounts of 50 - 75% on a wide selection of new and remanufactured radiators.