A Department of Energy study found that gasoline with 15 percent ethanol (E15) caused hotter operating temperatures, erratic running, and engine-part failure on smaller engines. Findings also revealed that gas with only 10 percent ethanol (E10) can help destroy engines.

Ethanol is an alcohol-based fuel made by fermenting and distilling starch crops, such as corn. It can also be made from "cellulosic biomass," such as trees and grasses.

Marv Klowak, global vice president of research and development for the largest manufacturer of small engines, Briggs & Stratton, said, "Ethanol has inherent properties that can cause corrosion of metal parts, to include carburetors and the degradation of plastic and rubber components. It can also reduced engine life and make them harder to start.”

Servicing dealers are reporting similar problems, even with E10. The EPA, which approved gasoline with 15 percent ethanol for use in cars year 2001 or newer, prohibits E15’s use due to the damage it causes in mowers and other power equipment.

"The higher the ethanol content, the more acute the effects,” according to the Outdoor Power Equipment Institute (OPEI). OPEI claims proposed warnings at pumps are insufficient. Customers will blame equipment makers should mowers and other outdoor gear fail because they were accidentally fueled with E15 gasoline.

Using gasoline with more than 10 percent ethanol has long voided most small-engine warranties but, until recently, the chance of doing so has been minimal. To be on the safe side, consider using ethanol-free fuel for smaller string trimmer and leaf blower engines.