This week, Ford and GM announced that they have approved the use of gasoline blends containing up to 15% ethanol for use in their later model cars and light trucks. This means the makers who produce more than a third of the cars and trucks on the road are pushing forward in linking 15% ethanol gas to their vehicles. The Japanese automakers Honda and Toyota and Nissan have not commented yet or taken an official position. It is also notable that Chrysler is resisting the change, advising through their owner's manuals that only ethanol gas blends up to E10 should be used in Chrysler vehicles.
Most auto manufacturers have opposed the blend, warning that gassing up with it will void their vehicle warranties. The auto industry has called for more testing of the new fuel, concerned about the effect a higher concentration of alcohol might have on vehicle engines. Indeed, the rejection of a legal challenge in August by the automakers to E15 appears to have paved the way for a change in their stance towards ethanol. GM is now approving E15 use in 2012 and 2013 model vehicles. Ford approves E15 use in the new 2013 models and, when asked, will admit that they will allow E15 use also in vehicles from 2010, 2011 and 2012.
But it's notable that the consensus among automakers is that they don't like E15 use in vehicles older than 2010. This is in contrast to the EPA's approval of the fuel in 2007 and later models. So who's right? GM will tell you that they don't like 15% ethanol in vehicles prior to 2010 because they performed specific tests with the ethanol blends in a variety of vehicles and found that E15 damages engines in those vehicles from model years 2001 to 2011.
When pressed, GM's recommendation is to consult your owner's manual for your particular vehicle. But since said owner's manuals only recommend ethanol use up to E10, that's GM's roundabout way of telling you not to use E15 without really telling you so.
This post was published on October 2, 2012 and was updated on January 5, 2017.