old as dirt wrote:
going from regular 100% gas to 10% added ethanol you did lose energy.
you lost 10%
your gas mileage suffered as well about 10% less.
Actually, with a 10% ethanol mix with gasoline (what we in the US call E10) he lost about 2164 BTUs/gallon compared to pure gasoline, which is roughly a 1.9% energy loss.
Pure gasoline: 114000 BTUs/gallon
E10 (10% ethanol): 111836 BTUs/gallon
You could probably lose 1.9% just by having your tires underinflated.
However, it is still wiser on older vehicles to stick with 100% pure gasoline, if only to prevent the seals and gaskets from eroding that are not ethanol resistant.