by Garrett McKinnon
VehicleMD Staff Writer
Originally published in Winter 2011 Issue

When you pull up to a fuel pump nowadays, you almost always come across a statement that reads: "This product may contain up to 10 percent ethanol by volume." So what does such a statement, and the use of such fuel, mean to you, the driver? Read on as we answer your ethanol-related questions.

What is ethanol?
Ethanol is an alcohol fuel derived from the fermentation of sugars and starches that is commonly used as an additive or replacement for petroleum-based fuels. In the United States, most ethanol is derived from corn, a renewable crop source. Why does my fuel contain ethanol? By law, oil companies must blend at least 5.9 percent ethanol with gasoline, a move mandated by the second Bush administration. Most blenders, owing to government subsidies, put as much as 10 percent ethanol in their gasoline, creating a mixture called E10. Recently, the government expanded the allowable concentration of ethanol in fuel to 15 percent (a formulation known as E15), though it cautions that drivers of older vehicles manufactured prior to 2007 should not use E15.

Certain vehicles known as "flex-fuel" are specially manufactured to use ethanol formulations up to 85 percent ethanol and 15 percent gasoline (a blend known as E85). Because ethanol is more caustic than gasoline, and thus harmful to certain seals and hoses commonly found in vehicles, only those vehicles manufactured to do so should use ethanol formulations above E10 or E15.

Is it safe for my car?
Generally speaking, ethanol formulations of E10 and E15 are safe for modern vehicles, though as mentioned previously, older vehicles should steer clear of E15. That said, ethanol-enriched fuels—in addition to causing no small amount of confusion at the pump—can create serious problems in some vehicles.

According to Mark Negast, technical director for Lucas Oil, if used incorrectly or in the wrong vehicle, ethanol fuels can cause rust and corrosion in fuel systems, can affect power output, can create deposits in engines and, in some cases, can soften rubber hoses.

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