The first thing I can say about fixing a radiator is--don't. The cost ofa racing radiator has come down over the last few years. For the mostpart, an aluminum racing radiator may now be less expensive than a brassOE type.

When a radiator core needs repairing, that usually means some of thetubes must be closed off. This will reduce the cooling capacity becausethe affected water passage tubes will no longer flow water. The amountof cooling reduction will depend on how many tubes are damaged.

For this article, a Howe Racing Radiator is being prepared. It suffereda substantial hit in a side tank and never leaked. However, when a boltwent through the tubes . . .

The positive side of repairing a damaged radiator is that you can returnit to action in about eight hours. Also, the repaired radiator can bekept in the hauler for a spare. When a radiator is damaged early in thenight, you will then have something to run in the feature.

The following fix is directed toward aluminum radiators, although I haveno doubt it will work on brass radiators, as well. Brass radiatorsshould be cleaned with lacquer thinner to remove the black paint in theaffected area.


The first step is cleaning. Grease, oil, or antifreeze must be cleanedfrom the damaged area. I use two different cleaners. The first isdenatured alcohol. (This is not rubbing alcohol, which contains variousamounts of water.) After the coolant is drained, pour some of thealcohol in the radiator. Turn the radiator so the alcohol runs out thedamaged area. This cleans the radiator from the inside.

Next, with the radiator sitting on a bucket, pour some of the alcoholover the damaged area. When this has evaporated, spray the area with anonflammable brand of brake cleaner such as Justice Brothers. The brakecleaner leaves no residue and removes any oil that might still bepresent. This cleanliness is important when using adhesives.

The next step is the tape. Yep, masking tape. I prefer the blue tapebecause it is easier to remove. Select the side of the radiator with theleast amount of damage. Lay the tape over the damage. You should tape amuch larger area than what might seem necessary. Rub the tape to make itstick, but don't bend the fins.

On the other side, using needle-nosed pliers, pull the damaged fins awayfrom the damaged tubes. If you can reach the tubes, crimp the ends withthe pliers. If you can't reach all the damage, that's OK as long as youdid a good job of cleaning.

Lay the taped side of the radiator down flat, preferably on some blocksso you can see under it. Under any conditions, the radiator should belevel.

Now you are ready to start making the patch. The active ingredient isJ-B Weld, a product of the J-B Weld Company, which makes two productsyou may be familiar with: J-B Weld and J-B Kwik. The J-B Kwik, whichsets up in four or five minutes, is as strong as J-B Weld but won't runin and fill the gaps as well because of the short setup time. For thesame reason, it doesn't have as much adhesion.

I have used J-B Weld for as long as it has been on the market. There area number of other two-part epoxy products available. I've never foundany to be, on all counts, the equal of J-B Weld. I have repaired engineblocks, cylinder heads, and hydraulic rams in garbage trucks with thestuff. If the metal is clean, J-B Weld works.

Although J-B Weld is the choice for our radiator repair, it is too thickto run down and fill all the leaks, usually hardening before it runs allthe way through. So we are going to modify our J-B Weld. After all, weare racers, and racers don't leave things stock. All two-part epoxiesthat I've used are soluble in alcohol; at least they are soluble beforethey harden. Therefore, alcohol can be used as a thinner and cleaner forepoxy. But it must be denatured alcohol, not rubbing alcohol.

Since pairs of 1-ounce tubes are the standard size found in stores (thecompany also makes 5-ounce size tubes), I picked up several packages.Styrofoam coffee cups make good mixing containers. Neither epoxy noralcohol melts the foam. Rather than squeezing my fingers to the bone, Icut off the bottom of the tubes, making the epoxy's exit much easier.Mixing two tubes at a time, I stirred until the color of the mix wasconstant. Then I added the alcohol. From the 1-gallon can of alcohol Ihad, I used one capful to thin one pair of tubes. When stirred well, themix has the consistency of honey. It will now pour into the damaged areaof the radiator. At this lower viscosity, the J-B Weld will fill all thecracks and crevices it can reach.

The J-B Weld hardening time is dependent on the temperature. It is muchfaster at 100 degrees than at 60 degrees. If you are working in colderclimates or in an air-conditioned shop (you lucky dog) consider warmingthe patch. The beginning of the warming procedure should have begun withthe tubes of epoxy. Don't get them hot, just warm. Once the patch iscomplete, warm the whole area. A hair dryer is fine for this.

I mentioned setting the radiator on some blocks so you could see underit. It won't hurt to point the hair dryer under there, too. There isanother advantage to having the radiator spaced up. If any epoxy leaksthrough the tape, it can be scraped up with a putty knife and reappliedto the top side.


Although I have never had a radiator leak using this method, I alwaystest the radiator. There are several ways to do this.

When you make the trip to the parts store for the J-B Weld, pick up acouple of rubber freeze plugs that will fit the radiator outlets. Theseare the type that expand by tightening the bolt in the middle. Use theseto plug the radiator outlets.

Method one: Use a testing radiator cap that seals against the topflange. Then pressurize the radiator through the overflow tube. If youpressurize the radiator, it must be done using a regulator in the airline. Do not use more pressure than the radiator will encounter inoperation. I don't advise more than 25 psi. Once the radiator ispressurized, it will need to be immersed in water where bubbles can beseen.

Method two: Use the two plugs for the outlets. Get a good radiator cap.Using a hand-squeeze vacuum pump attached to the overflow tube, pull agood vacuum on the radiator. Pinch off the vacuum line because theselittle pumps often leak back. Go eat lunch, watch a movie, or something.When you return, pull the hose off the radiator. If it still has vacuum,it should be OK. A crude repair, perhaps, but it has always worked forme.


A new radiator is always best. You can often repair one if damage is nottoo great. A repaired radiator such as this will not cool as well as anew one, but repaired radiators make good spares.

Clean the radiator well. Use J-B Weld thinned with denatured alcohol forthe repair. Test the radiator after repairing.

Contact Sleepy at:

J-B Weld Company Howe Racing Radiators