The overflow tank on your car is a necessary component of the engine coolant system. Excessive heat or accidental impact may rupture the plastic tank, rendering it useless. Removing the damaged tank and replacing it with a new one is probably the quickest way to fix this problem. If you cannot find a suitable replacement, cannot afford the additional expense, or would rather just fix the leak, grab a wrench. Then remove the damaged tank and fix it.
Rinse the tank inside and out with clear water. Pour a cup of bleach into the tank and shake the tank to distribute the bleach evenly. Soak a rag with the bleach inside of the tank. Wipe the outside of the tank with the bleach rag. Rinse the tank, and the rag, with clean water. Wipe the tank with a dry rag, turn it upside-down, and allow the tank to dry for two hours.
Hold the tank firmly and drill through each point in the crack. Place the drill bit next to the tank, pull the trigger, allow the drill to come to full speed, and press the bit against the tank. Continue holding even pressure on the drill until the bit emerges from the backside. Drill a hole at each end of every crack in the tank. Wipe away debris with a clean, dry rag.
Heat the area with your heat gun. Hold the nozzle of the gun 4 to 6 inches from the surface of the tank and pull the trigger. Move the gun back and forth the length of the crack. Continue heating the plastic until it begins to wilt.
Press the polyethylene strip against the heated surface and continue constant heating with your gun. Watch the strip while heating for signs of it melting into the crack. Press the strip with your putty knife to press the plastic into the crack and seal it. Allow the plastic to cool completely and trim the excess with your razor knife.
