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Radiator Leak Repair

One of the easiest ways to repair a broken radiator it to use a sealant, which will rapidly plug the holes on your radiator and prevent fluid from escaping. Using this easy, do it yourself method, you can avoid paying thousands of dollars at the mechanics shop. Here is everything you need to know about radiator leak repair.

First, it’s important to realize how dangerous a radiator leak can be. Over time, parts of every vehicle begin to break down, and a broken radiator can lead to overheating and fire risks, among other problems. As you can imagine, it’s important to stop a radiator leak as quickly as possible.

One of the fastest and easiest ways to stop a radiator leak is to use a rubber spray sealer like Flex Seal. These products will coat the surface of your radiator with a sheet of waterproof liquid rubber that will effectively protect your vehicle from the elements and prevent any further leakages. Here are the step-by-step instructions on how to repair your radiator leak using rubber spray sealer:

Supplies needed for radiator leak repair

  • A rubber spray sealer (we recommend Flex Seal for this purpose)
  • An old rag to wipe up any oil and sludge
  • A bucket of water that you can sink your radiator into (optional)

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The first thing you need to do is determine if you actually have a radiator leak.  Look for signs of coolant leakage on your parking spot, driveway, or garage floor. Next, take a peek inside the actual radiator (when your engine is cool) to see if the coolant is unusually low. If it is, then you may have a radiator leak.


Take a careful look at the radiator to find the spots where it could be leaking. This could be something as obvious as a pool of fluid, or it might be fairly minor, like green discoloration on the actual radiator. A hole or leak should be located fairly close to either of these two warning signs.

Sometimes, you still will not be able to find the holes in your radiator, in which case you should remove the radiator from the hood of your car and place it in a tank of water. By watching the bubbles flow upwards, you can determine where air is escaping from.


Take your rubber spray sealer and use it to patch up any holes you may find on the radiator. For larger holes, you may require a significant amount of rubber, while smaller holes will need only a quick burst. Simply point it at the hole and spray out a stream of liquid rubber, which will then attach itself to your radiator.


Wait for the rubber to dry and then check to see if any more fluid can leak out. If you’ve already removed the radiator from the hood of your car, then you might as well place it in a pool of water to check for air bubbles again.


Place the radiator back inside your car and refill it with cooling fluid. If everything has gone according to plan, then your car will be running in tip-top shape again. Congratulations! You’ve just avoided paying hundreds of dollars at a mechanic shop.

Why is Flex Seal the best rubber spray sealer to repair a radiator leak?

As mentioned above, we highly recommend using Flex Seal to repair your radiator leak. Due to its unique, fast-acting formula and easy-to-use technology, Flex Seal is clearly at the top of the rubber spray sealer industry. Here are just a few of the reasons why it is such a popular product:

  • Works on any surface: Unlike some spray sealers, which are designed to adhere to specific surfaces, Flex Seal will stick to virtually anything, and is especially good at sticking to the material on your radiator.
  • Long-lasting: Not only will it form a powerful bond with your radiator, but it sticks for an incredibly long time.
  • All-weather support: Even those who live in extreme climates can use Flex Seal on their vehicle. It works easily in temperatures from -60 to 300F, and is completely waterproof. Put simply, the durability of a product like Flex Seal is amazing.
  • Easy to use: I can’t think of a single car repair tool that is easier to use than Flex Seal. Using its slick, easy to use handle, you simply point and spray it at the problem that you want solved, and away it goes.
  • Affordable: With all of these features, you would think Flex Seal would cost more than $19.99. However, for that price, you get two big cans of rubber liquid rubber spray that can easily be applied to a number of different problems around your house. So, if you still have most of a can left after your radiator leak repair, you can use it to repair a leaky roof, broken faucet, cracked pottery, and so much more. The only limit is your imagination.

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