How to Dissolve Varnish From a Fuel Tank

Varnish inside of a gas tank, whether automobile or any other vehicle, generally results from poor quality gas, old gas that has sat in the tank for weeks or months, or chemical contamination. Excessive varnish will build up into a sludge-like film, sometimes thin or very thick. The varnish material can clog fuel filters, fuel lines, injectors and carburetor needle seats and bleed hole passages. A vehicle owner who wishes to dissolve the varnish from his tank should remove the tank from the vehicle for a more thorough inspection and cleaning procedure.

Instructions

1

Drain the gas tank of all possible gas by running it near empty, then use a hand siphon pump to remove the rest. Store the old gas in a certified safety container. To remove the tank from your vehicle, consult your owner's repair manual for the proper removal procedure. For an automotive tank, leave the filler neck and cap attached to provide an opening for the cleaning solution.

2

Use a floor jack and jack stands to lift and support the vehicle. Place the floor jack under the center of the tank for support. Remove the straps or tank mounting bolts with sockets and a wrench. Disconnect the electrical sending unit wires. Remove the vent and return fuel hose clamps with a screwdriver. Drop the tank with the floor jack and move it to an open area for cleaning. For a motorcycle or ATV tank, remove the tank mounting bolts, disconnect the fuel lines at the tank side and pull off any sending unit wires.

3

Remove the fuel pump module retaining ring (automotive in-tank pump) by tapping it counterclockwise with a hammer and center punch. Pull out the pump module. Direct a high-pressure hose nozzle in the tank filler inlet and spray the tank out for several minutes, removing any rust chunks or loose debris.

4

Tip the tank on end and let it drain into a safe waste container. Use duct tape to seal the tank openings; use rags to plug and tape the pump module hole. Place bolts in any attached hoses, or run tape around the nipple openings. Remove the gas cap. Put on safety goggles, gloves and a particle or respirator mask before handling any acid.

5

Fill the tank with enough water to wet the bottom with about 3 to 4 inches of water. Add one cup of muratic acid -- 2 cups for 16-gallon tanks or more. Replace the gas cap and sit the tank on end for 10 to 15 minutes, then re-position the tank to saturate another end. Let the acid work on all ends of the tank. Use an assistant to help you agitate and turn the tank several times. Drain the tank contents into a safety container. Repeat the steps until the solution comes out fairly clean.

6

Remove the gas cap and spray high-pressure water inside the tank. Slosh the interior and drain the contents. Remove the duct tape from the pump module hole, or unscrew the filler hose at the tank base inlet. Insert a small chain, such as a dog leash chain, or a heavy assortment of nuts, bolts and screws inside the tank.

7

Add 3 inches of water to the tank and 1 cup of muratic acid -- more acid for larger tanks. Reseal the opening with duct tape. Have an assistant help you shake the tank from all angles, letting the chain or bolts scrape and agitate the sides. Remove the gas cap and drain the tank.

8

Observe the contents of the acid. An orange or brown color denotes heavy varnish and sludge present. Repeat the agitation process, using clean water and fresh muratic acid. Repeat the agitation process until the acid and water solution is nearly clear. Remove the tape from the tank opening and spill out the chain or bolts and acid solution. Use high-pressure water to blast the inside of the tank. Set the tank on end to allow a thorough drip dry.

9

Inspect the interior of the tank with a flashlight. You should see no rust, orange or brown coloring. The inside should look shiny, indicating bare metal. Remove all tape plugs and rags from the openings. Reinstall the pump module ring, if you have removed one, by setting the module in place and tapping the ring clockwise with a hammer and center punch. Before tank installation, it is recommended that you use a tank sealer, which will coat and protect the tank interior from rust.

10

Install the tank sealer according to directions, coating the interior. Let the sealer dry and set, according to directions. Install the tank back on the vehicle in the reverse order of your dis-assembly. Fill the tank with enough fresh gas to get you to a gas station. Fill the tank.