by fuzzfactor | 2026-02-03 21:48:26+00:00
>Ethanol has a propensity to suck up ambient moisture and is more demanding of rubbers and happily attacks aluminum.

Actually, moisture problems are from using things like homemade alcohol or alcohol from unknown sources, where the likelihood of it already containing a sizable percentage of water has been a problem since the Model T days.

And if that water has a bit of an aggressive pH, it can have an effect on aluminum components.

This is just not a problem with gasoline-alcohol blends from reputable suppliers unless there is serious failure in the supply chain after that, where any fuel would have been contaminated by water regardless. The fuel-grade alcohol is tested before it is added, then the finished gasoline fully analyzed afterward.

Neither moisture nor corrosion is a problem with fuel ethanol or methanol, and when you see convincing information to the contrary (like from a pro mechanic) it often originates from misguided sources, "old wives' tales" for which actual evidence existed without being well-understood. But sometimes the most professional are the ones who don't take any chances, whether "common knowledge" is factual or not, if it doesn't hurt, no big deal.

Miscellaneous polymer compounds were the real question for cars that were not originally made for modern alcohol mixtures.

Ethanol just doesn't absorb moisture into your fuel tank by itself, even from a very humid environment.

Not any more than plain hydrocarbon fuel. In old ventilated fuel tanks, extreme temperature cycling under very humid conditions draws moist air into the tank when the fuel shrinks or is consumed. Kilos of cold fuel and cold metal can continue to condense moisture from the air, when the dew point is greater than the temperature of the tank. After a while you can get grams or ounces of water rolling around in the bottom of the tank. This could build up and stall out the vehicle or keep it from starting.

If it was only an ounce or two of water at the bottom of the tank full of all hydrocarbons, it would actually help to add a gallon of plain (good) alcohol to help dissolve the separated water into the gasoline so it can pass through harmlessly like it always has since gasoline has always had trace amounts of water anyway. Condensation is about as clean as rainwater so it's nothing the engine hasn't seen.

When most mechanics see something like this it has already gotten way out of hand, and there have been waves of anti-alcohol propaganda disseminated through time which reinforce the superstitious component.

Another problem from the '80's was when you do first start using alcohol-containing gasoline in an older car, it can break up varnish that has built up in the tank for years which never would come off until some alcohol came along. This could be a few grams, end up clogging the fuel filter, and the car stalls out no different than from water in the fuel line. Direct cause-and-effect relationship undeniably due to the use of alcohol, with many independent observations. Not a water problem, but who's keeping score.

Just not any more of a problem in the 21st century, similar conditions are so rarely encountered now.