The only possible harm could come if a highly concentrated mixture was induced into the system. Methanol, however, is highly corrosive even in moderate concentrations. Another possible side effect of changing over to ethanol blended fuels is the possible detergent action on an older vehicle's fuel tank and lines. In an extreme case, fuel filters could repeatedly clog until the system would be entirely cleansed of these contaminants. At present, this is the primary use for ethanol as an automotive fuel.
Ethanol contains NO sulphur.
Ecologically, this is one of ethanol's greater attributes. Decreased fuel economy is one of the greatest impediments to pure ethanol use. Based on the experience of the 1980's, to prevent fuel contamination, distributors must clean their system fuel supply before introducing ethanol blended fuels. New Transportation Fuels , American Petroleum Institute, Washington, D.C.-1991. A Report by the Union of Concerned Scientists, Cambridge, MA 1991.