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Several investigations have shown that the operation of spark ignition engines on methanol can cause unusually high levels of wear during conditions of warm-up and cold-weather operation. This engine wear occurs principally in the upper cylinder bore and ring are as, and corrosion plays an important role in the mechanism. The present study examines the theory that the corrosion is caused by combustion residues that form when liquid alcohol on the cylinder wall evaporates and burns. Combustion residues were found when shallow pools of alcohol fuels were burned in an apparatus designed to simulate a water-cooled cylinder wall. The residues contained water, alcohol, formaldehyde, acetaldehyde, formic acid, acetic acid, and methylenehydroxy-peroxide; they reacted rapidly with cast iron to form iron formate and FeO(OH). This study explains previous test results on cylinder bore and ring wear in methanol and ethanol fueled engines.