Ethanol is an alcohol, made from corn or grains, added to gasoline to oxygenate fuel at the gas pumps. Ethanol gasoline fuel is commonly called E10, E85, corn fuel, alcohol fuel and reformulated or renewable fuel and gas. More information: What is ethanol? Ethanol's History.
When using E10 ethanol alcohol fuels, several precautions are necessary because...
X E10 and E85 ethanol blend fuels have an affinity to quickly absorb amazing amounts of water.
X Ethanol alcohol is a great solvent, drying agent and cleanser, that can dissolve engine parts (rubber, plastic, aluminum, and certain fiberglass tanks), remove lubrication, and more. Engine seals and hoses shrink, swell, dry out and lose strength when exposed to ethanol renewable gasoline.
X Water is actually attracted and absorbed into an ethanol blended fuel, and phase separation occurs much sooner. With MTBE, ETBE, lead and other chemicals used in the past to oxygenate gasoline; this did not happen.
X The shelf life of ethanol blend fuels is much lower due to its water-absorbing and corrosive qualities. Replacing gasoline every 2 to 4 weeks is recommended with E10; Recommended use time guidelines vary due to several factors, including type of engine, atmospheric conditions of where engine lives or is stored, quality and octane of fuel, etc. 100 days is the maximum shelf-life for E10 gasoline under ideal conditions.
X The amount of ethanol blended in at the pumps, is not closely monitored. Checking gasoline meets safe and legal alcohol guidelines (10% or lower), is necessary now, until more stringent and consumer-friendly laws are passed.
With knowledge on ethanol's effects and necessary precautions, combined with careful monitoring, you can limit the problems and inconvenience of E10 gas for most engines.