- 1). Pop the Jetta's hood and view the radiator for leaks and their location, giving special attention to the seams, surfaces and the radiator cap. Also pay attention to the hose connectors. Cleaning the surface of the radiator with high pressure air or water will remove any debris that may be hiding a leak and its location. Alternatively, use a radiator pressure test kit to determine the location of leaks and to determine if the radiator cap is the source of the leak.
- 2). Stop the engine and allow it to cool. Replace the Jetta's radiator cap, as the cap cannot be repaired once the rubber seal malfunctions from becoming warped or torn. Alternatively, replace the rubber hose that may have deteriorated or may have been damaged by road debris. Replacing a radiator hose is fairly easy and can be accomplished by unscrewing the metal rings holding the hose in place. Make certain to clean the connectors before installing new hoses. While taping a ripped or torn radiator hose will create a temporary fix, the repair will not last very long and may create severe problems if the taped hose malfunctions while driving at high speeds.
- 3). Drain the radiator after cooling and remove it from the Jetta. Weld the surface hole in the radiator with commercial epoxy if the hole is fairly small and allow it to set for at least two hours. This method is referred to as a "cold weld," since no heat is involved when welding the radiator. Alternatively, use a radiator repair kit to weld a broken part or busted seam on the radiator. This process involves heating the broken piece or open seam and laying a plastic rod in the middle of the repair job. Heat the plastic rod until it melts into the seam or on one side of the broken part. Press the repair together and hold until it sticks. Allow time for the weld job to cool before placing the radiator back into the Jetta. Refill the Jetta's radiator and cooling system
- 4). Open the radiator. Pour one bottle or can of cooling system sealant into the radiator. Fill any room in the radiator with water or coolant and drive the vehicle for at least thirty minutes to allow the sealant to fill small leaks.