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2007 Gas Mileage: MFD vs. Purchased

Discussion in 'Gen 2 Prius Fuel Economy' started by aforkosh, Jan 1, 2008.

  1. aforkosh

    aforkosh Active Member

    Joined:
    Jan 2, 2004
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    Oakland, CA
    Vehicle:
    2023 Prius
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    Limited
    It's that time again. I filled my tank for the last time in 2007 and have now completed a spreadsheet for the annual mileage, computed from the MFD readings and my purchase log. I've conducted this exercise for the last 2 years. The 2006 post starts this thread and contains a link to the 2005 discussion that also describes the methodology used.

    This year, I did take some long trips in the car, and did not have long out of town flights (1 week of no Prius use in 2007 vs. 4 weeks in 2006), so my total mileage increased from 12958 miles to 15521 miles. However, overall, my mileage decreased from 48.3 to 47.5 via MFD and from 47.5 to 46.6 via purchase records. This was about a 2% differential. I posted several hypotheses for the difference last year.

    Mileage was particularly bad on my 1300 mile trip from the San Francisco Area to Death Valley in early December. I encountered headwinds on the journey down (normally tailwinds in that direction), and extremely heavy headwinds and cross winds associated with storminess in the area on leaving the Valley. Much of the trip in both directions was on rural and desert interstates where the defacto minimum speed is 70 mph, with the normal speed being closer to 80 mph. I stayed in the flow.

    I recomputed the annual figures subtracting the miles and gas for that trip, and the final numbers (48.1 for MFD and 47.3 for purchase records) were just slightly below the 2006 results. The remaining factor here was that I did replace my OEM tires in April with a new set of Goodyear Integrities. Although, they the same model, I believe that the increased tread of the new tires could cause a slight degradation in mileage.

    Note: Apparently the new forum software does not allow Excel spreadsheets as an attachment type. I have thus converted the spreadsheet into a zip archive.
     

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  2. barbaram

    barbaram Active Member

    Joined:
    Jan 24, 2006
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    Location:
    Trenton, NJ
    Vehicle:
    2010 Prius
    Model:
    IV
    Sounds like you did pretty well.
    Don't forget that ethanol has been sneaking into the gas blends and it does reduce mileage.
    Also the more I drive, the more it becomes apparent that tire inflation is really critical.