isopropyl alcohol could prevent water-contaminated fuel

Isopropyl alcohol could prevent water-contaminated fuel

By Dave Osmolski

With the coronavirus pandemic squarely upon us this spring, boating was curtailed during the worst possible season. With marinas and public and private boat launch ramps closed, many boats languished in boatyards and driveways.

I wonder how many boat owners, like me, were faced with water in our gasoline fuel tanks. Water collects due to condensation and ethanol additives absorbing water from the atmosphere, which has been going through periods of heating and cooling.

Pumping out and disposing of contaminated fuel can be an expensive proposition, but it can be avoided. While ethanol can contribute to contaminated fuel, other alcohols can re-disperse the water back into a burnable mixture. The most widely available alcohol to do this job is isopropyl alcohol. If you can find a source, isobutyl alcohol is also effective. With the increased demand for sanitizers, isopropyl alcohol may also be difficult to find.

Drugstores usually carry 70% solutions of isopropyl alcohol. Do not use this. Look in the hardware store where the solvents are sold for 99% isopropyl alcohol, also called isopropanol and IPA.

Isopropyl alcohol is also sold as a fuel additive. Read the labels on the additives at your automotive store. If you can’t find isopropyl alcohol, you may be able to get it labeled with a trade name as a fuel additive.

Isopropanol absorbs moisture from the air. This means that after restoring your fuel with an addition of isopropanol, you should run the remaining fuel through the engine by taking a long trip or enough laps around the lake to use up the fuel.

A few caveats are in order here. Isopropanol is said to be no more corrosive to rubber and other polymer parts of the fuel system than ethanol. It is less aggressive than methanol. Because it’s also a better cleaner than ethanol or methanol, it removes many deposits in a fuel system. I’m not certain if this will present problems or not. All the literature and testimonials I have read indicate no ill effects from this “cleaning,” but you should use at your own risk.

Isopropanol has an octane rating of 105. Depending on how much you use to re-disperse water in your fuel, the overall octane rating may change and affect the way your engine runs. For a typical 40-gallon fuel tank, one half to one pint of isopropanol will disperse the water and get your engine running satisfactorily.

The water that’s now dispersed in the fuel is said to actually improve engine performance. Years ago, when most fuel systems were carbureted, a device was sold that introduced a small amount of water vapor into the fuel/air mixture to improve performance.

Isopropanol, like most of its alcohol cousins, absorbs moisture from the air. This means that after restoring your fuel with an addition of isopropanol, you should run the remaining fuel through the engine by taking a long trip or enough laps around the lake to use up the fuel so you can fill up with fresh fuel.

I hope this information saves you the trouble of disposing of multiple gallons of water-contaminated fuel.


David H. Osmolski of Charlotte Power Squadron/27 has been repairing boats since high school when his first boat, a canvas-covered canoe with cedar ribs, leaked in gallons per minute and required constant repair.

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