My how-to for repairing leaking radiators

December 1, 2012 | By Richard Prince


Over the last 50 years I have fixed many leaking radiators. Here is my method: Obtain a bottle of powdered aluminum. This used to come in a plastic tube from GM dealers but I now use AlumAseal from Gold Eagle.

If you cannot find this at your local supply store, contact Gold Eagle directly for information on retailers in your area (

Get a box of Arm & Hammer powdered Washing Soda. Drain the radiator and block, remove all of the pipe plugs at the bottom of the block. Get replacement drain petcocks. Make sure to use a coat hanger wire to dig out what is behind the plugs. Then install new petcocks snugly but don’t over-tighten them.

You’ll be putting in two cups of Washing Soda mixed with warm water. Caution—this mixture is caustic and it will stain paint and chrome. Protect your paint and chrome plated surfaces! Put some clean water into the radiator, start the engine, and carefully and slowly add the soda mixture. Do not overfill! Remember, this solution is caustic!

Go for a 10-minute ride to get the water warm and thoroughly mixed. Upon returning, take off the radiator cap and open both petcocks. Drain the water onto a white cloth or towel to see all the junk that comes out. When the radiator is empty, remove the petcocks and run fresh water through the engine block. Repeat the procedure as required until the rinse water is clear.

Then add the sealer as per the instructions on the bottle.

For cracked blocks use KW Brand Block Sealer after cleaning the cooling system as described above.


Thank you for sharing your experience and technique with your fellow Auto Restorer readers. I’m not keen on recommending that people use caustic chemicals but if they do then I strongly urge them to wear protective gear, including chemical-resistant clothing and gloves, goggles and a respirator.

For what it’s worth, I’m also not a huge fan of additives designed to stop leaks. My concern is that the material obviously won’t confine itself to the leak, but will instead disperse throughout the entire cooling system. Can some of these products coat radiator and heater core tubes they pass through and act as an insulator that diminishes the effectiveness of the cooling system?

Having said this, I have used them in emergency situations and when the radiator leak was small they did work.

I have also used JB Weld (a two-part epoxy) to fix radiator leaks with notable success. I did this by locating the hole, thoroughly cleaning the area around it and then roughing the surface up with sandpaper. Apply a liberal layer of the epoxy product, feathering it out around the perimeter.