E15 fuel has been certified for sale in the United States and is slowly beginning to show up at filling stations. Here's a quick rundown of what you need to know about this new fuel option. What is E15 and why should I care? E15 is shorthand for gasoline blended with 15 percent ethanol. The reason it's a big deal is that ethanol is fairly corrosive to rubber and certain metals, so it can cause damage to vital components. Ethanol also attracts and bonds with water from the air, and that water can separate out inside the tank due to...