E85 is a mix of 85 percent ethanol and 15 percent gasoline. Unless your car or truck is designated as a “flex-fuel” vehicle you should not use E85. If you run E85 in older cars (pre-1995 that are designed for gasoline) then your car may be severely damaged. It can cause damage to seals and hoses along with causing corrosion throughout the fuel system. It can also wash lubrication off the engine’s cylinder walls. The hydroxyl group on the ethanol molecule is an extremely weak acid, but it can enhance corrosion for some natural materials.
For ethanol contaminated with larger amounts of water (i.e., approximately 11% water, 89% ethanol), considerable engine wear will occur. This wear is especially harsh during times while the engine is heating up to normal operating temperatures. Just after starting the engine low temperature partial combustion of the water-contaminated ethanol mixture takes place and causes engine wear. This wear, caused by water-contaminated E85, is the result of the combustion process of ethanol, water, and gasoline producing considerable amounts of formic acid (also known as methanoic acid). In addition to the production of formic acid occurring for water-contaminated E85, smaller amounts of acetaldehyde and acetic acid are also formed for water-contaminated ethanol combustion. Of these partial combustion products, formic acid is responsible for the majority of the rapid increase in engine wear.
Engines specifically designed for flex fuels employ soft nitride coatings on their internal metal parts to provide resistance to formic acid wear in the event of water contamination of E85 fuel. Also, the use of lubricant oil (motor oil) containing an acid neutralizer is necessary to prevent the damage of oil-lubricated engine parts in the event of water contamination of fuel. Since older cars are not protected from formic acid the use of E85 is not recommended.