Quote:
Originally Posted by 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.
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Every fill up is a reasonable time to reset since it give you enough mile/kilometers to get a decent average. As long as you are doing the same driving each time though. If I got gas and reset and drove around stop and go traffic it will give me totally different reading than if I reset and went on a 300 mile highway road trip. Both would be accurate according to the type of driving but may not be my "normal" average.