How to Fix a Radiator Leak with J-B Weld

Updated February 21, 2017

Radiator leaks cause the coolant level of your vehicle to drop. Low fluid levels increase the internal temperature of your vehicle's engine. Increased heat can cause warping of the engine components, resulting in expensive damages. Promptly repairing a radiator leak with J-B Weld will keep coolant inside of the radiator rather than on the ground without expensive repairs. J-B Weld consists of two-parts, when mixed the parts harden to a steel like consistency that permanently bonds to the radiator.

Remove dirt from the area around the radiator leak with a wire brush. Sand the area around the leak with 80-grit sandpaper to roughen the surface of the radiator.

Pour acetone on a rag. Wipe the sanded area with the rag to remove oil and grease from the radiator.

Squeeze equal parts of both the red and black tubes into a disposable plastic container. Mix the J-B Weld components with a wood stir stick. Stir until the mixture is one solid colour.

Apply the mixed J-B Weld to the radiator leak with the wood stir stick.

Pull the hose running off the overflow tank connected to the radiator. Push the line onto a vacuum line port on the engine. Start the vehicle. Let the vehicle run for 10 to 15 seconds. Turn off the vehicle. Connect the hose to the overflow tank.

Look at the repaired area. The J-B Weld should have a slight indentation where the vacuum pulled it into the leak.

Allow the J-B Weld to cure for 24 hours before using the vehicle.


Avoid burns, wait for the engine to cool before repairing a radiator leak.

Things You'll Need

  • Wire brush
  • 80-grit sandpaper
  • Acetone
  • Rag
  • J-B Weld
  • Disposable plastic container
  • Wood mixing stick
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