On 'Pure' Gasoline, Your Mileage May Vary: What's The Difference?

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Non-ethanol gasoline pump

Non-ethanol gasoline pump

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Unless you're the type to very closely read the fine print on the face of fuel pumps, you might not know that the vast majority of U.S. gasoline is truly ten-percent home grown—that's ten-percent ethanol, and with that ethanol almost certainly from corn.

The upsides of adding more ethanol to fuel include a reduced reliance on foreign petroleum production and reduced emissions of some air pollutants. Ethanol also raises gasoline's octane rating without the greater use of some of ingredients that may be more harmful to the environment (or to people).

But the primary downside of adding more ethanol to fuel—aside from issues relating to corn crops and food supply—is that it lowers the actual energy content of gasoline. According to the U.S. EPA, vehicles will typically get three to four percent fewer miles per gallon on E10 than on what it terms 'straight gasoline.' And of course, those are extra gallons of ethanol that you'll need to truck around the country.

Lower mileage...but how much lower?

The three-to-four-percent figure is what's widely accepted by the industry; on the other hand, the American Coalition for Ethanol found, through their own study, found that E10 only lowers mpg by about 1.5 percent on average.

On older vehicles, the affects of ethanol are a little more pronounced. Especially in vehicles from the 1980s and earlier, rubber-containing components such as gaskets, seals, and fuel lines can harden and fail earlier when run on ethanol-containing fuel, according to restorers, mechanics, and classic-car enthusiasts. Vehicles built in 2001 or later have already been approved for 15-percent ethanol, though.

Non-ethanol gasoline pump

Non-ethanol gasoline pump

Enlarge Photo
And the proliferation of E10 in just about every neighborhood, suburb, and truck-stop gas pump has led some classic-car owners—along with some other enthusiasts seeking better mileage or better performance—to go out of their ways for 'pure gasoline.'

In all fairness, that's not the right term. All gasoline is a blend of ingredients and compounds—like toluene, xylene, pentane, butane, heptane, napthalene, isopentane, and others—and ethanol can be one of them.

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