Since the early 1990s the US government amended the Clean Air Act to require the use of oxygenated gasoline to lower toxic emissions. This was accomplished with an additive called MTBE. Until in 1995 California found high levels of MTBE in drinking water. Ethanol was considered a safer replacement for MTBE and since then gasolines now contains ethanol.
Small amounts of ethanol are considered safe to run in most vehicles. However, ethanol is more corrosive and burns hotter than gasoline which could cause some engines to misfire, stall or overheat. It also emits more nitrous oxide and formaldehyde than gasoline and could potentially damage fuel pumps, lines, fittings and tanks.
In recent years the EPA has required higher and higher levels of ethanol in gasoline. Most gas is now 10% ethanol (E10) and the EPA is now authorizing up to 15% ethanol (E15).
The EPA says 15% ethanol is not safe to use in car and truck engines older than 2001 and not safe in smaller engines like lawnmowers, snowmobiles, motorcycles or boats.
Vehicle manufacturers have taken issue with the higher ethanol blends and are saying their vehicles are not designed to operate on 15% ethanol and the new gas blend will damage the engine. Some have gone as far as putting warning labels on their newer cars.
If your vehicle is not certified by the manufacturer to operate on an E15 ethanol blend, make sure you know the level of ethanol in the gas you use or you might be paying for that engine repair yourself.