Most modern motorcycles use plastic or composite gas tanks but those who ride older bikes (2000 and earlier) or have a vintage model from the 70s or 80s restoration project in the works, use metal tanks.
And metal rusts.
That would be a great band name. Metal Rusts! Anyway, a rusty fuel tank not only looks awful but if left untreated can contaminate the fuel and clog the carburetor. If you catch the rust early you can stop it in its tracks and continue using the tank once resolved. Wait too long then the metal becomes compromised, and you'll need a replacement.
How pray tell does a metal gas tank filled with fuel rust? Doesn't the gasoline prevent rust from forming? Yes, but don't forget condensation can form in low fuel levels and those who don't ride a lot or leave their motorcycle sitting for long periods of time with little to no fuel in the tank greatly increase the odds of rust forming.
Mechanic's Tip: Use pure gas and avoid ethanol-based fuel to prevent moisture build-up. When storing use a fuel stabilizer in ethanol-based gas or keep the tank filled with the pure stuff.
Often, rust shows from the outside but sometimes the outside of the tank looks good with rust lingering on the inside. How do I know rust formed on the inside of the tank?
- Fuel left sitting in the tank emits a metallic smell
- When fueling you might see pieces of rust briefly float near the filler port
- Clogged fuel filter or carburetor. Pieces of rust break off and flow into the fuel system.
- You hear larger broken pieces of rust "tapping" against the metal tank as you ride.
You can use a flashlight to peer inside the tank along with small mirrors to visually check the sides for confirmation. Either way, the following tips focus on removing internal rust but also applies to removing external rust.
Motorcycle Gas Tank Rust Removal
You will need:
- Rust remover
- Nuts and bolts
- Acetone or isopropyl alcohol
- Distilled water
- Rubber plugs or tape
- Gloves and goggles
- Fuel stabilizer
How to Remove Rust from a Motorcycle Gas Tank
In a well-ventilated area, drain all the fuel from the tank. Either ride it dry or remove the fuel lines and drain into a clean container. (Yes, you can reuse the gas but better burned off in your lawn mower or some other gas-powered garden tool) The forgetful type should label lines and wires for easy reinstallation. Now remove the tank and remove anything attached to the tank: petcock, fuel cap, etc.
Wash the Gas Tank
Wash the tank using soap and water. Say what? Relax. Use dish soap or something similar and hot water. Thoroughly rinse with contaminant-free distilled water and set out to dry. Once dry, toss in a handful of clean nuts and bolts with distilled water then seal all openings with rubber plugs or heavy-duty waterproof tape. Shake vigorously for 10 minutes or so. The nuts and bolts "clean" the tank and dislodge rust particles. After shaking, remove nuts and bolts and rinse again with distilled water.
Motorcycle Gas Tank Rust Remover
Commercial products work but since we don't sell any and we want to save you money - grab some vinegar! Fill the tank about three-quarters full with vinegar (add some baking soda for an explosive cleaning!) and leave overnight while periodically shaking the tank to ensure thorough coverage.
Rinse the tank and add baking soda to neutralize any leftover vinegar. Rinse thoroughly with distilled water until the water runs clear.
For external rust, sand the affected areas first then apply a baking soda vinegar mixture or your favorite rust dissolver. Rinse thoroughly. Apply as paste of baking soda to neutralize the remaining vinegar and rinse again. For deeper or extensive rust, you might need a sander and something stronger than vinegar and baking soda.
Afterwards, apply a protective wax, clear coat or paint to prevent wax from returning.
How to Prevent Flash Rust in a Motorcycle Gas Tank
Pour some acetone (or isopropyl alcohol) inside the tank, swirl it around and dump out. Acetone removes any remaining water, enhances the drying time and prevents flash rust which often occurs in metal gas tanks after cleaning. (You can use acetone for a quicker drying process after the initial cleaning, too if you want.) Thoroughly drying avoids future rust formation. Leave the tank in the sun to dry if you don't have acetone.
How to Prevent Rust from Returning
Add a fuel stabilizer to some gas and swish around the tank to fully coat the inside. The stabilizer helps prevent future rust issues by preventing moisture build-up. Drain the mixture. You can also apply a tank sealer which creates a protective barrier, a more involved process, and perhaps the subject of a future article.
As for the outside of the tank, apply a rust-inhibiting primer and follow with an enamel or epoxy based paint or powder coat the thing. An extra layer of clear coat over the paint adds additional protection and, like your car, apply wax every now and then.
Install the tank, reattach the fuel line, petcock and anything else that fixes to the tank. Tighten all connections. Fill the tank with fresh fuel (It's a small tank, pay for the pure gas!) and check for leaks. Now go for a rust free ride!
Not too much of a pain! You won't "git 'er dun" in half an hour but pop your favorite sport on the boob tube (hopefully Motocross) and get started. If the tank appears compromised in any way because of excess rust, buy a new one. We have plastic versions but for vintage restoration you will need to check the internets.
