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3 Best Epoxy For Plastic Radiator Repair

The radiator in your vehicle is what keeps your engine cool and it’s vital to its health. However, things happen and your radiator may begin to leak due to damage. So what are you supposed to do in this situation?

Do you pay somebody to repair it? Do you replace the whole thing? Both of these options are going to cost a pretty penny. However, one solution that can save you a lot of money and hassle is to repair the hole yourself. 

You may be wondering how you can fix it yourself, especially if you’re a novice mechanic or have never even touched the inside of under the hood. Well, for a plastic radiator leak, we suggest an epoxy. Here are some of the best epoxy products for plastic radiator repair. 

J-B Weld 2120 Radiator and Plastic Repair Kit

Top Epoxy For Plastic Radiator Repair

1.JB-Weld PLastic Radiator Repair

Oh, JB-Weld, how we mechanics love you. JB-Weld offers a variety of products that help keep your vehicle in top-notch running condition. We’re pretty sure that most of the cars on the road older than 1995 are held together by JB-Weld. So what do they have to offer now? Their radiator and plastic repair kit for starters. 


The JB-Weld radiator repair kit is fairly simple to use. You don’t have to bother taking out the radiator to repair it if you can easily access the problem area. As long as the hole is less ¼” in diameter or less or the crack is 4” or less, this paste can fix it. The kit comes with the putty, a fiberglass cloth, sandpaper, and an applicator. 


JB-Weld putty is extremely durable. It takes 4-6 hours at room temperature to set and the full cure takes 15-24 hours. It has a tensile strength of 3960 PSI and it can hold up to temperatures of 550 degrees Fahrenheit when it’s completely cured. 

J-B Weld 2120 Radiator and Plastic Repair Kit


  • More affordable than replacing the radiator
  • Strong bond
  • Great for DIYers and mechanics
  • Easy to use


  • May begin to set quicker than expected
  • Requires expanding the crack to completely fill it
  • Not a permanent solution

2.K-Seal Coolant Leak Repair

If you don’t have a ton of money to spend on a new radiator, then you won’t want to buy a product that is going to make the problem reoccur.

You’ll want something that you can use that will repair the leak once and then never have to worry about it again, at least not for a long time. This is where K-Seal Coolant Leak Repair comes in handy. 


K-Seal is a versatile product. It’s one of the few epoxys that meet ASTM D3147 standard. Additionally, it’s not only used to stop radiator leaks, but it can repair a heater core, water pump casings, and freeze plugs. 

Easy to Use

Unlike JB-Weld, you don’t have to mix K-Seal. WIth JB-Weld you have to mix the epoxy together and it may begin to set quickly. With K-Seal, all you have to do is shake the bottle quick and pour the mixture into the radiator.

Once that’s done, you can add heat to the radiator to speed up the drying process. You can do this by simply starting your engine. You don’t even need to drain the radiator. 

Safe & Scientifically Tested

This product is safe and effective. It can repair a leak of just 1/32 of an inch. Once it has cured, it can withstand the extremely high pressure that comes from the combustion chamber without clogging the system or causing it to faily.

K-Seal ST5501 Multi Purpose One Step Permanent Coolant Leak Repair


  • NNo mixing needed
  • Resistant to heat and pressure
  • Doesn’t affect performance
  • Versatile
  • Can seal 1/32” holes


  • Reports of the leak coming back

3.Permatex Permapoxy Black Plastic Weld

Sometimes the epoxy that you have to mix with tools can be a bit too much to deal with and you may not even obtain the proper consistency. Not to mention, it could begin to set even before you get it onto the radiator. However, this isn’t the case with Permatex. 

Easy to Use

Rather than having to use tools to mix or dealing with runny liquids, Permatex can easily be mixed right on the back of your hands. It has a putty consistency that’s thick and you can knead it without the risk of drying. 

This epoxy is also heat resistant and can withstand temperatures up to 300 degrees Fahrenheit and 600 PSI. 

Quick Set

Once the bond has been mixed, you can simply apply an even coat to the hole or crack. It only takes around 25-minutes to set, as opposed to 24-hours. This type of epoxy that dries quickly is much more convenient than the others that require more time. You can simply patch the hole and be on your way in half an hour. 

Permatex 84145 Permapoxy Black Plastic Weld - 0.84 fl. oz.


  • Quick drying
  • Easy to mix
  • Affordable
  • Won’t clog 


  • Doesn’t bond polyethylene

What Makes The Best Epoxy?

There are plenty of things to consider before you buy epoxy for your radiator. There are plenty of them out there, especially from JB-Weld, but are they the best? What exactly makes them the best? Let’s go over a few things. 

Ease of Use

Radiator epoxy can come in a variety of forms. Most of them will have two or three components that require mixing. You may even have to shake what’s in a bottle. Some may need to be kneaded. You should always take into consideration what situation you are in.

Which epoxy is most compatible? If it’s an emergency, you’ll want a quick-drying epoxy, such as the Permatex Permapoxy. If you don’t want to get your hands dirty, consider the K-seal. Aren’t in a rush? Go for JB-Weld. 


An epoxy is meant to stop the problem, not create more. Besides being durable and hard setting, an epoxy should also be able to breathe. The epoxy needs to have a certain amount of airflow that can get through it.

If you put on an epoxy that is going to block airflow on a larger crack or hole, it could put a damper on the performance of your radiator. Look for an epoxy that can handle the pressure, won’t clog, and won’t snap. 

Water & Heat Resistant

It’s going to cost you a little more money, but you should consider an epoxy that’s going to be water resistant. When some epoxys come in contact with water, they can slide right off of the holr or crack you patched. 

Additionally, you should find an epoxy that can withstand excessive heat. Yes, an epoxy sets faster when heat is applied, but after that, if exposed to excessive heat, it will fall off. A good quality epoxy will stay on no matter how hot it gets. 

Quick Setting

Lastly, make sure it’s quick setting if you’re in a pinch. Some of the best epoxies for a plastic radiator will set in just a few hours. You can also find some that may set in just a few minutes, such as the Permatex which sets in just 25-minutes. 

Epoxies that don’t cure quickly can have you waiting hours or even days to use your car again. This is why it’s important to find a product that will have you back on the road in no time, unless you have nowhere to go and don’t care about time. 

Gorilla 2 Part Epoxy, 5 Minute Set, .85 Ounce Syringe, Clear, (Pack of 2) - 4200130

Types of Epoxies

No, not all epoxies are created equally. There are actually two different types of epoxies for plastic radiators: one-component and two-component epoxies. 


One-component epoxies are the best to use if you don’t want to get your hands dirty. It requires absolutely no mixing on your part and no accessories. All you do is give the bottle a shake and you’re all set. This kind of epoxy also sets at higher temperatures. 

You should also know that one-component epoxy is also resistant to high temperatures, durable, and weather resistant. 


Two-component epoxy is a little more difficult to deal with than one-component because it requires mixing it before it sets. You have to perform the process rather quickly or you’re wasting your money. However, these kinds are flexible and can bond, coat, and seal. This kind of epoxy would be similar to JB-Weld products. 

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