cement to repair crack in Honda radiator

It's probably Nylon (poly amide) with some type of filler.

charlie_r is correct. But I doubt you can weld it so that it will withstand the thermal expansion and the internal pressure it will see in use.

I believe that the tanks are bonded to the heat exchanger with an adhesive. But they have an engineered interface and perfect bonding conditions with lots of surface area.

Call a radiator shop and ask them if they can do it. Then you'll know if it's feasible.

Good luck.

Thanks to all who responded. I spent several hours searching for answers on the web and discovered that Charlie and Lych are correct. The tank material is probably glass fiber reinforced nylon which is resistant to most chemicals and can not be solvent welded. The only approach is to heat weld the cracked area and melt a nylon rod to fill the gap. That requires expensive tools I don't have. The local radiator shops recommended against trying to repair the radiator crack-because the repair usually fails-and I have decided to replace the radiator.

Dennis Waller

Good Choice.

Heat is your enemy here. Nylon is easy to get adhesion to, but the adhesive will not handle the temperature's very well. You could try using a novolac based coating to repair it. Superior Environmental makes some repair materials that will probably handle the heat. The key is in surface preparation. I would recommend cleaning the area with degreaser, then acetone. Sand with 80 grit sandpaper, and blow it down. Hit it with acetone again. Apply the repair compound or coating, let it cure until it is tacky as tape, then coat it again. Then let it cure for at least 24 hours. It will not cure completely for 72 hours so if you can, wait. Then you should be able to fill the tank and let it rip. If you have any small leaks add some black pepper to the anti-freeze and you could have a good repair. Nylon is a thermoset plastic, it cannot be welded it can only be repaired with adhesives. Cheers, Bloefeld

"Nylon is a thermoset plastic, it cannot be welded it can only be repaired with adhesives." This will come as a shock to a huge number of plastic chemists, resin manufacturers, plastic molders, and others who have been using it as a thermoplastic all these years [successfully, too!]. See http://www.physchem.co.za/OB12-sys/polymer2.htm for example.

Still, replacement is probably the best "repair" for this situation - though I have had methacrylate adhesive (Plexus MA300, I believe) hold for months after I cut to expose a clean surface (VW radiator, not Honda).

You make a good point because Nylon can be both thermoset and thermoplastic. As a thermoset sort of person I think of nylon as a plural component system. However, it is clear that its highest use is in thermoplastic injection molding. However, that said my solution will work well, adhesion by epoxy to nylon can be achieved with little additional effort. Using novolac based resins can give enough heat resistance to do the job at the 200 to 300F range that I think this application would work well on. I also agree that just replacing the part with a good used part will be the safest and easiest solution. Thanks for setting me right about this matter. Cheers, Bloefeld

Can you provide a reference or link to a thermoset Nylon? I can imagine that use of certain catalysts or methods in cast Nylon might make it a poor candidate for susequent reheating and melting, or that mixed/alloyed chemistries (polyamide-imide?) might do so, but none of the sites I checked while confirming my recollection mention such a thing. I do know that some plastics come in both types (polyurethane, I believe, is one such), but haven't encountered a Nylon thermoset. I'd still expect a header tank to be injection molded, rather than cast, to speed production.

Thanks!

Back in the past we used many epoxy/poly amide thermoset resins to put military/space stuff together.

I think that's where the thermoset comes in.

Where did you get that idea? Nylon is a thermoplast but there are many varieties and the higher molecular weight ones have high melting points.

Check first to see if the tank is a thermoplast by applying a hot soldering iron to a non critical area if it melts you have a thermoplast. it could then be possible if the crack is small or narrow to use the soldering iron to weld the parts together. If there was some sprue or other non critical part of the plastic this might serve as a "solder".

Otherwise you have a problem but if the tank is a thermoset then you will need to make a key by roughing up the surface - making cuts across the crack will be the best. staples could also help but you will need to see that perforations are sealed. An epoxy could be the best solution but a cyanoacrylate might be worth trying. In either case the use of a fine glass fibre (surfacing tissue) would be recommended

"Where did you get that idea? Nylon is a thermoplast . . . " [in reference to post 10, which claims that Nylon is a thermoset]

I've already tried twice (posts #9 and #13) to call him on that statement in post #10, with no success. Good luck!

"An epoxy could be the best solution but a cyanoacrylate might be worth trying."

At least some cyanoacrylates are heat- and water-sensitive, especially long-term, and unfilled grades often cannot fill gaps. A methacrylate might be a better choice (and I have used Plexus MA300 in radiator repair, and even on a reservoir for power-steering fluid that I believe was polypropylene; still holding at 6+ years - probably only because I have a replacement tank on the shelf!). Some of the thickened gap-filler cyanoacrylates might still work, but I'd check manufacturer's specifications scrupulously before bothering to try.

Strange ideas - some folks cannot understand the difference!

Nylon is polymerised to the hardness required it is then thermoformed but can also be machined to a final shape. There is no further chemical change after it is produced. They can be recycled.

Thermosets are chemically converted into higher polymers in the moulding process and will not melt - cannot be recycled.

Cyanoacrylates chemically convert on exposure to moisture. Irreversible - not recyclable - but I think they are only employed as adhesives.

Once you replace the rad, you might try welding the cracked one using a soldering iron/gun. I have had some success using that method on plastics, but never on a radiator.

charlie r is correct. If you have to get by for a short time until the new radiator is shipped, sand clean and epoxy. reinforce with window screen, and reapply the epoxy. Make sure the epoxy is designed for radiators. Try leaving the radiator cap loose to prevent pressure buildup.

The real question that I have is why did the tank break in the first place. Most of the time that I have seen a radiator tank suddenly crack was because of a defective thermostat. If your radiator was not broken by something hitting it, replace your thermostat. It's cheap insurance. Good luck.

It should have a recycling symbol on it, and that code will tell you the material. However, the material may be exotic. If not, it is probably polypropylene and very difficult to bond.

I doubt it is PP. I think the rest of the group is correct in assuming it to be a nylon derivative. However, one can bond PP by running a flame over the bond area right before applying the adhesive. The adhesive must have the lowest surface energy one can find. 3M makes an few very good epoxies that bond well to polyolefins. They are costly though and in this particular case it would likely be cheaper to just find a junked radiator. Cheers, Bloefeld

I gave a very comprehensive answer to using epoxy. I pointed out that just any 5 minute epoxy was going to prove worthless. I gave detailed instructions on the preparation of the substrate and the source of supply of epoxy systems that would stand the best chance of working. I do not understand why simply saying sand it and use epoxy with window screen warrants a good answer when my frankly better solution does not. Window screen is not a reinforcement. If you believe that you need more tensile than the 12,500 - 22,000 psi that my solution gives, use a layer of fiberglass sail-cloth to reinforce the area. This will give you 30,000 psi put is unnecessary given the low pressures involved. One thing that I should have added to my preparation instructions was to wave a blow torch over the repair area. This will effectively flame-treat the substrate for a few minutes and create higher surface energy on the plastic. Doing this creates polar bonding sites for the novolac to chemically bond to. Using standard epoxy that one gets in those little tubes will do little to solve the problem because they will lose 50% of their physical properties at 200F. Cheers, Bloefeld

Re: "I do not understand why simply saying ~...~ warrants a good answer..."

Perhaps 'twas the "cheap insurance" suggestion which followed that statement...

Cheers

I do not understand why simply saying sand it and use epoxy with window screen warrants a good answer when my frankly better solution does not.

I agree, bloefeld, I have offered many superior comments (he says with tongue-in-cheek), and have not received good answer credits, either. And, so it goes. :-)

There is some confusion about nylon. It is both a thermoplastic material in some applications and a thermo-set material in others. It can be injection molded, reaction molded, or cast. It just depends on how it is going to be used. In the case of the radiator cover, if it is made of nylon it is most certainly injection molded because the part-turn around using any other method would be too long. Regardless this site http://www2.dupont.com/Plastics/en_US/index.html is helpful in understanding nylon. It discusses both thermoplastic nylons and thermo-set nylons. The difference between the two is simple. Thermoplastics can be melted again and reformed into a different product. Thermosets simply melt or burn when heated, they cannot be reduced to their component parts. Thermoplastic plastics can usually be welded, however many are difficult to weld without highly specialized techniques. Thermoset plastics usually cannot be welded. They are more properly assembled and repaired using thermoset adhesives to do the work. Cheers, Bloefeld

You clearly have a better answer to the procedures needed to repair a plastic radiator. The only part of my answer that I consider unique, and possibly deserving of the GA was the reasoning for the crack that I shared, and the preventive measures that might prevent a reoccurence.

I have been awarded GAs for stupid remarks that I have made, and been ignored for what I have thought were truly good answers. If I was a better comedian, I might have more GAs.

Enjoy the site. Laugh every day. Contribute your knowledge. We all share from wise people like you. There are some very knowledgeable people here. Please share your knowledge with us, and forget about collecting GAs. The rewards are the people that you will come into contact with, and every once and a while, knowing that you have helped someone else. Some times with a smile, sometimes with a solution. Good health to you.

Now that it's too late I seem to remember that we used Hexafluoroacetone sesquihydrate to solvent bond thermoplastic polyamide (Nylon).

That was years ago. Seems that there was a warning on the container that exposure to the liquid had been shown to cause testicular cancer in mice.

I agree that replacement is your best option (as you have wisely done).

Hypothetically, I would think a repair using plastic welding with a reinforcing strap welded over the repair would be pretty permanent.

I wouldn't trust just the weld alone as the nylon is probably filled for extra strength (not to mention reduced cost, nylon isn't cheap).

A test for nylon is to touch with a hot piece of steel. Withdraw the steel piece. If you get a long piece of plastic pulling out with it, the material is probably nylon.

I've lost it now, but about 40 years ago Shell plastics had a very useful guide to plastics which included similar simple tests to get a rough guide as to what plastic you were dealing with.

It also had a useful set of tables giving indicative properties.

I haven't seen anything similar since.

JB Weld is hands down !

What material will permanently repair a 3" logitudinal crack in the top of a 1991 Honda Civic radiator?

Depending on where you live, multiple pieces of paper approximately 6" X 2 1/2", imprinted with portraits of men, women or even birds, along with mysterious words and images and various numbers.

Sorry this thread has deteriorated into an arguing contest. NOTHING will 'permanently repair' such a large crack. The tank material has failed. Even if you could bond a reinforcing/sealing' patch over the crack, it is highly probable the entire tank has weakened and another crack or even 'catastrophic' failure is imminent.

Bite the bullet and order a new radiator for Radiators.com or other on-line supplier. All metal (copper) radiators are not expensive like Dealer prices for Japanese cars.

Very true - but there are idiots like me who are chronic fixers and like to have a go.

If it is a thermoplastic - easy to find out with a soldering iron there is a vague chance that you can weld the joint - did it with the water-wash bottle on my car ( Opel - spares are a rip-off).. Otherwise chuck it out as suggested and visit a scrap yard.