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

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

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

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

The following fix is directed toward aluminum radiators, although I have no doubt it will work on brass radiators, as well. Brass radiators should be cleaned with lacquer thinner to remove the black paint in the affected area.

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

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

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

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

Lay the taped side of the radiator down flat, preferably on some blocks so you can see under it. Under any conditions, the radiator should be level.

Now you are ready to start making the patch. The active ingredient is J-B Weld, a product of the J-B Weld Company, which makes two products you may be familiar with: J-B Weld and J-B Kwik. The J-B Kwik, which sets up in four or five minutes, is as strong as J-B Weld but won't run in and fill the gaps as well because of the short setup time. For the same 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 are a number of other two-part epoxy products available. I've never found any to be, on all counts, the equal of J-B Weld. I have repaired engine blocks, cylinder heads, and hydraulic rams in garbage trucks with the stuff. If the metal is clean, J-B Weld works.

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

Since pairs of 1-ounce tubes are the standard size found in stores (the company also makes 5-ounce size tubes), I picked up several packages. Styrofoam coffee cups make good mixing containers. Neither epoxy nor alcohol melts the foam. Rather than squeezing my fingers to the bone, I cut 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 was constant. Then I added the alcohol. From the 1-gallon can of alcohol I had, I used one capful to thin one pair of tubes. When stirred well, the mix has the consistency of honey. It will now pour into the damaged area of the radiator. At this lower viscosity, the J-B Weld will fill all the cracks and crevices it can reach.

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

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

Although I have never had a radiator leak using this method, I always test 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 a couple of rubber freeze plugs that will fit the radiator outlets. These are the type that expand by tightening the bolt in the middle. Use these to plug the radiator outlets.

Method one: Use a testing radiator cap that seals against the top flange. Then pressurize the radiator through the overflow tube. If you pressurize the radiator, it must be done using a regulator in the air line. Do not use more pressure than the radiator will encounter in operation. I don't advise more than 25 psi. Once the radiator is pressurized, it will need to be immersed in water where bubbles can be seen.

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 a good vacuum on the radiator. Pinch off the vacuum line because these little 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 for me.

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

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

J-B Weld Company Howe Racing Radiators
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