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MFD MPG Calculation

Discussion in 'Gen 2 Prius Technical Discussion' started by Winston, Oct 30, 2007.

  1. Winston

    Winston Member

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    I track all of my fill ups and compare the mpg shown on the display with the mpg calculated based on the amount of gas put into the tank. I reset the MFD MPG indicator every time I fill up. I know that there will be descrepancies between the two mpg calculations on individual tanks, but they should balance out over time.

    I have data for the first 11,500 miles on my Prius. I weighted the mpg values based on the number of miles and calculated an error percentage between the two mpg readings. My calcs show that the MFD mpg averages 1.3% higher than the true calculated mpg.

    Anyone else do that calculation?
     
    #1 Winston, Oct 30, 2007
  2. qbee42

    qbee42 My other car is a boat

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    That is well within the normal error reported by other users.

    Tom
     
    #2 qbee42, Oct 30, 2007
  3. PA Prius

    PA Prius Active Member

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    As you can see from my signature mine MFD also runs a bit high. Since the "actual" bounces around quite a bit due to the bladder I think my true mileage is about 1 mpg less than is shown on the MFD.

    PA P
     
    #3 PA Prius, Oct 30, 2007
  4. dhancock

    dhancock 2 Prius Family

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    Ours runs 2.1% high (compared to actual consumption based on ODO milage).
     
    #4 dhancock, Oct 31, 2007
  5. Highly ImPriused

    Highly ImPriused Impressive Member

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    At just over 12,000 miles, my weighted average MFD reading (50.7 mpg) is 2.4% higher than calculated (miles driven/total gallons in = 49.6 mpg).
     
    #5 Highly ImPriused, Nov 2, 2007
  6. patsparks

    patsparks An Aussie perspective

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    1 to 2% is pretty good, as good as most gauges.
     
    #6 patsparks, Nov 2, 2007
  7. personallyuneek

    personallyuneek Yankee fan in New England

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    Based on the fact that ODO trip A/b readings stop at 1/10 miles and seem to round up, the % seems to make sense over time.

    I have a -.5 average MPG difference (My MFD reading is .5 Mpg higher that ODO trip B/Actual Gal) over my first 2000 miles
     
    #7 personallyuneek, Nov 15, 2007
  8. richard schumacher

    richard schumacher shortbus driver

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    Without a truly independent measure there's no way to know how much of the discrepancy is due to MFD inaccuracy, and how much is due to gas pump inaccuracy. Almost everyone reports the MFD value as higher than the manually calculated value. By some odd coincidence any amount of this discrepancy which is caused by the gas pump would be in the gas seller's favor. 2% is within the error allowed by most states' weights and measures inspectors.
     
    #8 richard schumacher, Nov 15, 2007
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