Fuel Tank Liner:
Seal, Restore or
Replace the Tank?

What a fuel tank liner actually does

Steel and terne-plate tanks rust from the inside because they rarely stay full and dry. Air in the empty space carries moisture, it condenses on the cold steel overnight, and water ends up in the bottom of the tank. Modern fuel makes that worse in a stored vehicle. Most gasoline in the US is E10, and ethanol absorbs water. NREL testing summarized for the Renewable Fuels Association found E10 holds a little over 0.4% water by volume at 60°F, but only 0.25% at -20°F. Past that point the ethanol and water drop out of the gasoline together as a separate layer on the tank floor, right where the rust starts.

A liner puts a fuel-resistant film between that water and the steel. It does three things:

• Locks down what is left of the rust after cleaning and etching, so scale stops breaking loose and clogging screens, filters and carburetor jets.
• Seals pinholes and porous seams. Damon Industries says Red-Kote will seal leaks up to 1/32 inch (about 1 mm); anything larger should be soldered or welded first by a radiator or tank shop.
• Slows future corrosion on a tank that will sit for long stretches, which is exactly the life most motorcycles, tractors, boats and collector cars lead.

What a liner does not do is restore metal that is gone. It is a few thousandths of an inch thick. It will not hold a tank together where the seams have split or the bottom has thinned to lace, and it will not stick to grease, varnish, loose rust or an old coating that is lifting. Every liner maker says the same thing in different words: preparation is the job, the sealer is the easy part.

Fuel tank liner products compared

The liners and services we see most on motorcycle, tractor, marine and classic car tanks. Figures are what each maker or test states; where none is published, we say so. Click a header to sort.

Two things stand out. First, coverage rules differ by a factor of two, so buy for the product you are using, not a forum rule of thumb. Second, cure time is the step people cut short. Damon Industries is blunt about it: add fuel before Red-Kote is fully cured and the curing stops for good. A Classic Motorsports reader who lines tanks regularly said he lets sealer dry at least a week before the tank goes back on. We agree with him; nothing about a tank job rewards hurrying the last step.

How to line a fuel tank so it stays put

Every kit has its own chemistry, so the instructions on the can win over anything here. The sequence below is what all of them have in common, plus the habits we have picked up from decades of coating metal that has to stay coated.

1. Pull the tank and strip it bare

   Drain it outdoors, remove the sender, pickup, petcock and filler neck, and plug or tape every opening except one. Liners and their etching solutions damage paint, so Eastwood tells you to protect or plan to refinish the outside.

2. Knock loose rust free

   Damon Industries suggests a rubber mallet or a length of chain or gravel shaken around inside to break scale loose. Pour it out and repeat until nothing more comes out.

3. Degrease

   Varnish and old fuel residue are the main reason liners do not stick. Red-Kote's instructions call for a water-soluble detergent at about 2 ounces per gallon of tank capacity; kits like POR-15 include a dedicated cleaner degreaser. Slosh hot solution on every surface, then rinse.

4. Etch the metal

   A phosphoric or similar metal prep converts the rust that is left and gives the liner something to grip. Eastwood's process sloshes each surface for 5 to 10 minutes until the steel turns a uniform gray. Never let the tank sit and flash rust between steps.

5. Dry it completely

   This is where most failures start. Rinse, then dry with warm air until there is no trace of water, which Damon Industries says can take 1 to 12 hours depending on method. Some kits finish with an acetone rinse to pull out the last moisture. Eastwood keeps drying air at 1 to 5 psi.

6. Pour, roll, rest, repeat

   Pour the liner in, rotate the tank so it wets every surface including the top, and let it stand 8 to 10 minutes on each side before turning again (KREEM and Eastwood both use that interval). Drain the excess out of the fuel outlet so it cannot pool and skin over.

7. Open the outlet and clear passages

   Before the film sets, blow out the petcock threads, pickup and vent so they are not sealed shut. A liner that skins over a small outlet or vent is a common and avoidable mistake.

8. Cure it longer than the label minimum

   Leave every opening open for airflow at 60°F or warmer. Labels range from 8 to 48 hours; we would rather wait several days. Then reinstall with a new inline filter and check it after the first few tanks of fuel.

Bulk fuel tanks: coatings that belong outside

We get this question weekly: can you spray ArmorThane polyurea or a bedliner inside a gas tank? For a vehicle tank, our answer is no. Our spray polyureas are built for abrasion, impact, waterproofing and many chemical exposures, but a vehicle fuel tank is constant immersion in a changing blend of gasoline, ethanol and water, sealed in a space you cannot inspect. That calls for a liner formulated and tested for it, applied as a thin, even film you can pour and drain. A thick, fast-set spray coating is the wrong tool for the inside of a 4 gallon motorcycle tank.

Where polyurea earns its place is around fuel, especially once storage gets bigger than a vehicle:

• Tank exteriors, saddles and straps. Steel tanks rust from the outside where water sits under straps and on the bottom. A primed polyurea system stops that. See our corrosion prevention coatings.
• Secondary containment. Under EPA's SPCC rule, a facility with more than 1,320 gallons of aboveground oil storage in containers of 55 gallons or larger needs a spill prevention plan, and secondary containment is part of it. Lining concrete or steel dikes is core work for our applicators; see fuel containment, storage tank containment and EnviroThane modified polyurea.
• Transfer tank beds and fuel islands. Truck beds that carry fuel transfer tanks take a beating from straps and spills. A spray-on bedliner handles that; compare options on our spray-on bedliners page.
• Underbody steel near the tank. Frames, crossmembers and tank skid plates rust under road salt. Our truck undercoating guide covers what works there, and our guide to finding undercoating near you covers choosing the shop.

The interior lining of large petroleum storage tanks is a different discipline altogether. It is engineered work, guided by industry practice such as API RP 652 for tank bottom linings and specified by the owner's engineer. Talk to us about the containment and exterior, and to a qualified tank lining contractor about the interior.