How to clean a rusty fuel tank
A rusty fuel tank can put the brakes on your motorcycle, moped, or powersports restoration project. But don’t worry! Cleaning a rusty fuel tank can be as simple as raiding your pantry and your drawer of spare hardware.
Lowered values, clogged fuel filters, poor performance and even a damaged engine can result if the rust is not cleaned out. The corrosive ethanol in today's fuels has made this problem even more prevalent.
As an overview to clean your tank you need to:
Assessing your tank
The condition of your tank will determine where you start. Light to moderate surface rust can be cleaned very easily. However, things can take a turn for the worse if the tank is starting to rust through. Inspect the tank. Especially around the areas of the seams or where fluid can settle. Small pin holes can be repaired multiple ways. Even a good sealer can deal with that. But larger holes will require an experienced welder and a good paint job.
The tank here has moderate surface rust and should clean up well.
Look into your options
There are several options for cleaning out the scale. First determine if you want to do it yourself or hire a pro to get the job done. Many radiator shops specialize in cleaning and lining fuel tanks. This could be a great option if you simply want it done for you.
To do it yourself, you can choose from a variety of options. You will typically need some kind of acid to chemically clean and etch the tank and some mechanical agitator to help with the corrosion removal.
For an acid, a great DIY source is regular vinegar which is cost effective, strong enough to cut through moderate rust, but still safe enough for your paint job. It is also safe and easy to dispose of.
Popular cleaners such as EvapoRust or Metal Rescue are also excellent cleaners and will work faster than vinegar, but come at a higher cost.
Muriatic and phosphoric acids are a possible choice, but are very caustic and can damage paint and your health. They also require dilution to use and even more dilution to dispose of.
Use caution if you go this route. The only advantage of these options is speed. The risks are apparent and therefore, not recommended for the casual mechanic.
There are likewise many choices for agitators. Regular old nuts and bolts, BB’s, sheet metal screws, or even a length of chain. The important things here are to make sure the agitator does not react to the acid and that you can get all of the hardware out.
For this tank, I used vinegar and random hardware and even some change to get this done on the cheap.
Prepare your tank
The first step is to remove the tank from your bike. Then remove the petcock and plug all the holes. Silicone plugs, vacuum caps, and rubber stoppers can all be of great use here. Know that this process can also damage your fuel cap so you might want to remove that as well.
Add the chemical and mechanical agitator
With the holes in the tank plugged you can now add your acid. Top up the tank and be sure to leave room for the agitator that you’ve already assured won’t react violently with the acid.
Pour about a handful or two of your agitator into the tank. Use common sense here as large metal pieces will damage your tank. You also may want to have some sort of count or measure for your agitator. You want to make sure what goes in will come out. Again, a length of chain is not a bad idea here as it’s easy to get it all out.
This is where the hard work comes in. You need to shake the tank several times over the course of several days or even a few weeks. This is largely dependent on how badly the tank is rusted and the strength of the acid you are using. The process is simple: pick up the tank shake until you are out of breath, set it down, and repeat it later- up to a few times a day. You know you are done when you start to see bright metal inside of the fuel tank. Once the tank has achieved your level of cleanliness, then you know you are done.
Flush and neutralize
Now, remove the plugs and dump the acid and agitator into a bucket. Be sure the bucket won’t be damaged by the acid and to dispose of the acid properly. Strong acid will need to be diluted for disposal.
The next step is to rinse out all of the acid with a hose. Run water through the tank and shake it around to make sure all of the acid and agitator comes out.
Again, plug the holes in the tank and add some dish soap and very hot water to neutralize any remaining acid. The hot water will evaporate more quickly than cold water. Remove all of the plugs and let air run through to get rid of the water. A hair dryer or heat gun can speed this process. Just be careful as the heat can damage paint.
The goal here is to work quickly to avoid flash rust. A little may form and that is fine.
This one turned out well.
This final stage is optional. Some people opt for the additional sealer. RedKote, Caswell, and Kreem are common commercial choices. Some people swear by them, others hate them. The issue is that a bad seal job can cause more problems than a rusty tank and can damage a tank beyond repair.
Another short term seal method to stop flash rust from forming is to plug the tank back up and pour in a little kerosene and shake it around. If the tank is going to sit for awhile, you can coat the inside with some tacky two stroke oil.
Keeping your tank full of fuel and using the bike regularly are the best defenses against rust in the tank. Rust formation requires air and a full tank will keep the air out. Using the bike regularly will keep fresh fuel sloshing around the tank to keep air and moisture away.
As you can see there are many ways to refurbish the inside of your tank. Choose the best method that suits your skills, budget, and will get the job done.