[MuseChaser]

I reset the avg mpg and trip odometer A every time I fill the tank, and also keep a running spreadsheet calculating actual miles driven divided by gallons required at fillup. Over three years and abot 50K personally-driven miles (currently car has 71k on it...bought it used), the car-calculated display has been consistently slightly more than 1 mpg optimistic than actual. My mpg has also decreased slightly, from a best of 40mpg hwy/33mpg routine use during th first year of ownership to about 35mpg hwy/28 mpg routine use this past year. No explanation.