I personally run 89.5 on my 2.5L. As this is the octane that ethnaol is in iowa. Since I run ethonal all the time this is not a problem, however ethonal cleans out your fuel system so it can clog fuel filters and other stuff. the plus side of ethonal is it keeps water vapor out of your system. With my 89.5 octane ethonal my 2.5L automatic averages 27mpg and that with me an 18 year old male driving. P.S. my driving stlye is aggressive.

1998 mercury Mystique 2.5L with that stupid slush box only engine mod so far a optimized tb dark blue with midnight blue leather interior finnaly got rid of the door ding guards and pinstripe