Rust and other corrosion of a gas tank can lead to engine problems and eventual engine failure, and holes in the tank can render it unusable. You can fix both of these problems by using a sealant to seal the inside of the gas tank. Water and other oxidizing materials won't be able to touch the metal of the tank in order to rust it; and holes will be filled with the sealant, which will then harden. Sealing a gas tank should take as little as two days, including cleaning and drying time.
Remove the gas tank from the vehicle using a screwdriver or ratchet (depending on how the tank is attached.)
Cover any holes in the tank with duct tape to prevent the cleaning agents or sealant from leaking out. If there is loose rust on the edges of the holes, use your screwdriver or a file to break it free.
Pour 1 pint of acetone into the tank, rotating the tank to coat the inside. Pour out any excess acetone, then remove the duct tape and allow the tank to dry completely.
Place new duct tape on the tank if needed to cover any holes, then pour the rust remover into the tank. If the rust remover is concentrated, mix it with 1 gallon of water beforehand. Allow the remover to remain in the tank for up to one day, depending on package instructions. Rotate the tank every two to four hours to allow the chemical to reach any rust that might be in the tank.
Empty the tank, then rinse it with clean water to wash away any remaining rust remover. Remove the duct tape and allow the tank to dry again.
Place a handful of screws into the tank, and shake the tank vigorously for two minutes to break loose any remaining rust. Make sure that all of the screws you placed into the tank come back out.
Put more duct tape over any holes in the tank, then add 1 pint of acetone again. Rotate the tank to allow the acetone to coat it completely, then drain and remove the duct tape. Allow the tank to dry once again.
Cover the holes with duct tape one last time. Use putty or clay to close the outlet holes to the tank.
Mix the sealant according to package directions, making sure to mix for at least one to two minutes if using an epoxy sealer. Remove one of the putty plugs, pour the sealant into the tank and replace the plug.
Rotate the tank to ensure that the sealant covers the entire inside surface of the gas tank. Remove one of the plugs and drain any excess sealant from the tank.
Let the tank sit for seven to ten minutes. If your gas tank features a built-in fuel filter, use a pressurized air hose to blow a burst of air through the fuel line port in order to remove sealant from the filter itself.
Remove all putty caps after one hour, scraping away any excess sealant on the outlets with a knife. Place the gas tank in a warm location where it may cure for one day (or three to five days if the tank will be used for alcohol-based fuels.)
Reinstall the gas tank.
