With a 10% ethanol gasoline, you must make the change for good - by not going back and forth from regular gasoline to ethanol and then back to regular gasoline between fillups.
After the first tank or two of the ethanol mix, you've got to change your fuel filter, as the ethanol will clean out the particles and gunk that were in the system, therefore plugging the fuel filter and cutting the fuel flow.
With an E-85 mix, beware! Detroit makes specific engines that are made to burn E-85 , and this information is in the vehicles data. The engine seals are different. In an engine that is not made for E-85 (or higher) the fuel will eventually dissolve the seals in the engine, which is EXPENSIVE to fix.
GringoCArlos - using 10% ethanol since about 1980, (well at least until 1994 when I left for good),and my pappy now burns E-85.