One aspect I would advice for those trying to maximize fuel efficiency is to get one of the obd gauges like a scangauge
or an ultragauge
. I've got both but prefer the display of the ultragauge and the cost is a bit better, however, either is fine. Several displays to chose from but instantaneous gas mileage is the most critical to help modify driving style. The focus does have an instantaneous bar graph display but it's not as helpful as seeing numbers. Another plus to the ultragauge for earlier second generations without the ambient temperature display (like mine) is it's one of the available gauges.