Cleaning Your Gas Tank

Carburetor technical help: cleaning your gas tank

Removing and cleaning an old dirty fuel tank can, indeed, be a problem. Actually, it can be several problems rolled into one. Those problems include discovery of what you need cleaned out, whether it is built-up varnish, rust, or both. Then there is the problem of whether the tank is sound enough to withstand the cleaning and still not leak. But assuming all these variables are working in your favor, and you have decided against simply replacing the tank, then here are a few tips on ways to clean your classic car’s fuel tank.

You have some alternatives to choose among. First, there are professional shops that could take care of your problem. Radiator shops will sometimes take in fuel tanks to be boiled out with chemical solutions. Or you could do it yourself, either with similar chemicals or with somewhat safer options. There are numerous commercial products that are designed specifically for this task. And then there is the fully home-made route.

Problems exist and must be overcome with any method. Electrolysis will not clean in and around the internal baffles. Acids can damage the metal, particularly if it is weak or thin already, and if the tank is not immediately sealed internally, the walls can begin to rust again in very short order. Water-based solutions have to be completely evacuated and the tank thoroughly dried or you are introducing not only water into your fuel, but encouraging rust to return very quickly. Objects placed in the tank to dislodge rust must be removed completely.

Muriatic acid is sometimes touted for rust removal, but it is a dangerous substance, both in liquid form and with the vapors it gives off. And it may not be the best thing for some of your fuel tank’s components. Muriatic acid is a weak hydrochloric acid, and any chlorides that remain in your tank will quickly encourage corrosion. Muriatic acid is mainly a de-rusting chemical, far less effective on the varnish and sludge. For cars with an openly displayed fuel tank, if you drip some of this stuff on your shiny paint job, you can kiss the shine goodbye. The same warning applies to acetone. Plain white vinegar is a safer alternative for rust removal, but vinegar is 95 percent water, so rinsing and thorough drying are called for–and it takes longer to do the same work.


1. Replace the tank. This is a good choice particularly if you do not know how sound the tank will be after being cleaned. When the rust and sludge are removed, you may discover holes you were unaware of, and wind up spending the money to clean it and then replace it anyway. Still, some classics’ gas tanks are going to be VERY expensive, so trying to clean the old tank may be wise.

2. Abrasive blasting. Many shops perform this service, and it is fast and not too expensive. You may want to find a shop that utilizes CO2 instead of sand or steel particles. The CO2 evaporates leaving no residue.

3. For sludge and varnish, denatured alcohol, also known as methylated spirits, might be your best alternative. It is inexpensive, readily available, and contains no water or other substances that conflict with gasoline. Of course, the sludge it loosens must all be removed. Fill the tank about one third full (so it isn’t too heavy), and shake that thing. Put on some music. It isn’t all that bad. You can strain it through a shop towel and then pour back the strained alcohol for another round of shaking. And don’t forget ventilation. Acetone and lacquer thinner also effectively cut the varnish, but are a little more expensive and less compatible with gasoline.

4. Ethanol. Yes, the same ethanol that is not so great to run through your classic car’s fuel lines and carburetor happens to be reasonably good at loosening the sludge in fuel tanks. To avoid its inherent problems for classic cars, use it as a tank cleaner, not a fuel. But it is still not quite as effective as denatured alcohol.

5. For rust removal in the absence of built-up sludge, muriatic acid works quite well, as does vinegar. But the most important factor may be mechanical loosening of the rust with an object inserted in the tank before shaking. A chain may work best of all. People have recommended using loose nuts and bolts, BB shot, gravel, and all sorts of things, but nothing is as easy to remove completely as a length of dog chain. It knocks the rust off the inside of a shaken tank and then comes out of the tank with little effort.

Some people advocate automatic shaking devices. They can work well, but you do need to monitor them. A thin wall of metal after the rust is dislodged can be fragile enough to get a hole punched in it without too much effort. Manual shaking is still best.

6. Sealing the tank. If you decide to seal the interior of the tank instead of, or in addition to, cleaning it out, there are several products that work pretty well. Some of them come in multi-purpose kits that both clean and seal the tank. Examples you may wish to consider are the Bill Hirsch kit, and a product named POR-15. But be cautious with similar products, as some may still not be ethanol-resistant, so you could be pouring an additional problem into your tank. Read the label.

Ethanol Additive

Other important notes:

Simply draining the bad gas in a tank only gets rid of the liquid gas, not the sludge it leaves behind on the walls of your tank. That stuff can become a problem that you don’t need.

Old gasoline does not just smell bad, it can make you sick if you work around it for long without proper ventilation. Take precautions and be safe. You may actually need your brain at some point.

Expensive repairs can be avoided if you pay attention to the quality of the fuel your engine receives. A temporary in-line fuel filter may be a great idea after cleaning your tank, just to be able to monitor what is flowing through that line. Carry a spare for on-the-road emergencies.

Contaminants from a dirty fuel tank can quickly spell the death of your carburetor. And if you are buying a new carburetor it might last a very short time if you don’t also make certain the gas tank that feeds it is clean.

Your fuel is the lifeblood of your car’s performance and longevity. Give it the treatment it deserves and your car will give you the performance you deserve.

Updated on 12/29/2020

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