How To Prevent Rust Buildup In A Fuel Tank

One of the quickest ways to ruin a day is to experience a crank no start phenomenon when eagerly hoping to go on a ride. This can be caused by a variety of factors, but today we are focusing on the fuel system of your motorcycle.

Modern motorcycle fuel tanks are typically made of either metal or plastic. Modern plastics technology has come a long way and can hold fuel without breaking down or chemically reacting in a negative way that might damage the bike.

When talking about rust, we will be referring to a motorcycle with a metal fuel tank. It goes without saying that rust is created in a reaction involving metal, so bikes with plastic tanks stay clear of this concern.

There are some practical steps that can be taken to avoid rust development in your metal fuel tank to keep you bike running as it should.

In general, rust buildup in a motorcycle fuel tank can be prevented by not letting fuel sit for an extended period or by adding a fuel stabilizer before extended storage. Also, if your metal gas tank has been damaged in a crash or tip over, empty the tank then make a repair or replace the tank before reintroducing fuel.

Why Does Rust Develop Inside My Tank?

You may be reading this article because you are planning on leaving your bike in the garage for a while or you just purchased an old bike that has been sitting for an undefined period of time. In either case, it’s important to know why rust will develop in these circumstances.

All fuels mixtures regardless of the grade or octane contain a certain percentage of water. Although small, over time this water will separate and begin to oxidize your metal tank. Some of the water will escape through condensation, while the rest that separates will sit on the bottom of the tank.

This is bad for two reasons:

  1. There is now a high concentration of water directly contacting one of the bottom of your fuel tank. Water sinks to the bottom of the solution as it is more dense than the gas. This will begin a chemical reaction and eventually form rust and contaminate your gas. If left for long enough, the tank will form a leak as the rust will eat through the metal.
  2. When you first start your bike after a long stint of sitting, the engine will get a big gulp of water first before any fuel. This is very bad because you do not want a lot of water inside the combustion chamber. During normal operation, the percentage of water in the fuel entering the combustion chamber is negligible, so this isn’t a concern.

All in all, time is our biggest enemy here and this gives us the primary red flag to look out for when considering if our motorcycle has hidden rust inside the tank. This is going to be an issue with seasonal riders or track riders where the bike might sit for months at a time between riding periods.

Another reason rust might develop is from damage to the tank. Sometimes, either from external damage or excessive exposure to the elements, the outside of the tank can rust and wear through. This will allow additional moisture inside the tank and expedite this process.

How Can I Stop My Tank From Getting Rusty?

There are several ways to prolong the life of your fuel tank. In a perfect world, a motorcycle fuel tank will never have to be replaced or repaired if proper maintenance measures are taken.

There are three main actions you can take to prevent rust formation inside your fuel tank:

  1. Start Your Bike Regularly: Circulating the fuel through the fuel pump, injectors, and engine will help keep the gasoline solution from separating. If you’re not an active rider, go start the bike and let it run for a few minutes once a week at a minimum. There’s no science governing this timeframe, but if you let gas sit in a clear jar you will notice that’s about how long it takes for the solution to begin separating.
  2. Pour In A Fuel Stabilizer: The purpose of a stabilizer is to fight against fuel separation and metal corrosion. It is a combination of additives specifically designed to prevent rust formation if you know your bike will be sitting for an extended period. I would use the week timeframe again to make a judgement call about the use of an additive. If you know you’re going on a 10-day cruise next week, go ahead and buy some cheap insurance in the form of a fuel additive from a name brand company.
  3. Keep Tank Full Of High-Octane Fuel: If you keep your tank completely full of fuel, there will be less room around the top for condensation to form. Also, the higher the octane the lower the alcohol content. This will reduce the water threat and extend the length of time the fuel can sit without risk.

It is worth noting that not all gas is made equal. There is a chance that cheaper gas in more rural areas may contain higher levels of contaminates and water which would exacerbate this problem.

I have personally seen this before on the automotive side. If you take a fuel sample from a tank of ”farm gas” versus gas from a name brand station in a city, you will most likely see a higher concentration of water.

Additionally, on this same side note, if you by chance use a gas station that hasn’t been filled in a while, you may be filling up with fuel from the bottom of the gas station holding tank. While not always the case, this fuel may have an increased amount of contaminates or water as well. This won’t create rust if the vehicle is being used regularly, but it’s not good for the powertrain in general.

There are some “fringe” measures that can be taken if you are overly concerned about rust forming in your tank and it’s keeping you up at night. One of which is a gas tank coating product that you would apply to the inside of an empty tank. The idea here is that this will seal up any imperfections inside the tank and cover up any vulnerable sections that might have excess wear.

I personally have zero experience with anything like this but the idea makes sense. I would think this would be practical if I bought an old bike and wanted to save the tank rather than replacing it. Before applying any coating, the tank would need to be cleaned thoroughly.

The last thing I will mention here is full removal of the fuel tank for storage. This would only be practical or reasonable if you know your bike is going into storage for years with nobody available to start it up periodically.

When storing an empty tank, make sure it is completely empty and dry. I would recommend hanging it if possible and maybe throw in a couple silica packets to absorb any moisture left behind.

How Do I Determine The Condition Of My Gas Tank?

You might find yourself unsure about the condition of your gas tank. This will be most likely when purchasing an older bike with limited history.

It is also possible that you live in an area with a limited riding season and the bike has been sitting for months waiting for the sun to come out. Or you are a track rider and it’s been months since your bike came off of the trailer.

The first thing I would do in any of these situations if I was unsure of the fuel system status would be to smell the fuel inside the tank.

The difference between good gas and stale is noticeable and pungent.

This would be a good initial assessment because it is free, quick, and simple. If you are unsure of what bad gas smells like, go fill up a gas can with good gas and give it a whiff.

If your fuel fails the sniff test, then it is worth removing and draining the tank then visually inspecting the inside with a flashlight. If the gas is stale then it has definitely broken down and separated to the point where water has had a chance to do some damage.

Please use good judgement here. If you bought a 1978 Kawasaki KZ1000 that has rust all over the outside, lets skip the testing and just perform a repair or replacement of the fuel tank.

We also want to perform an exterior inspection of the gas tank. Check the seams, corners, and flanges for any exposed metal sections that may have rusted through. Bikes that have been left outside exposed to the elements their whole life will have extra wear in some uncommon places.

I’ve seen tanks develop rust around the fuel cap flange and the base of the tank where the fuel pump assembly attaches. It’s worth including this on an inspection after purchasing a new-to-you bike.

There Is Rust In My Tank…What Now?

You have concluded that indeed rust has infected your fuel tank and the bike cannot be ridden. Repairs of some sort must be made and now it’s time to weigh the options.

As mentioned above, some situations don’t warrant any option other than replacement. If you have a barn find on your hands, you might spend so much time performing a tank restoration that the price of a new tank would have been happily paid.

Let’s say the tank is unavailable to replace or you simply have more time than money.

Start by emptying and removing the tank. Using a light or camera, you can visually determine the scale of the damage. You will also want to take time to make sure no portions of the tank have worn all the way through. You would then need to treat the tank with a coating that will renew the metal surface and protect from future corrosion.

Before reinstalling a restored tank and filling with fresh gas, make sure it has sat long enough to fully fry and cure. Our main objective is to make sure no contaminates enter the fuel system and engine.

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