Difference between displayed and actual MPG

Discussion in 'Gen 3 Prius Fuel Economy' started by Vman455, Oct 2, 2020.

  1. Vman455

    Vman455 Active Member

    Joined:
    Feb 8, 2014
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    Location:
    Champaign, IL
    Vehicle:
    2013 Prius
    Model:
    Two
    Ever since I bought my Prius, nearly 7 years ago now, I've tracked the fuel consumption on Ecomodder, which calculates actual MPG from gallons replaced and distance driven. I have also recorded the displayed MPG for each tank. At just over 90,000 miles, that means 178 tanks with calculated and displayed MPG data.

    I put it all in an Excel spreadsheet and calculated mean, median, quartiles, and outliers for actual difference and percent difference for each tank. The outliers were few; 2 low values when the display showed less MPG than actual, an artifact of the reality that gas pumps are not 100% consistent. That left 176 "good" values for each statistic.

    The results:

    [​IMG]

    Mean = 3.04 MPG difference
    Min = 0.9 MPG difference
    Max = 5.3 MPG difference
    Median = 3.0 MPG difference

    [​IMG]

    Mean = 5.563% difference
    Min = 1.44% difference
    Max = 10.23% difference
    Median = 5.58% difference

    So, on my car at least the display averages +3.0 MPG high, or 5.6%.
     
    DimitrisTS and Pluggo like this.
  2. Kenny94945

    Kenny94945 Active Member

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    Vehicle:
    2016 Prius v wagon
    Model:
    Four
    Wow.
    Awesome data.
    7 yrs, 90K mile, 178 fill ups.

    If I understand correctly, the conclusion:
    Dash display if 5.58% higher than actual.
    Actual miles vs dash is 3.0 mpg lower.

    Just awesome.
    Thank you.
     
  3. Vman455

    Vman455 Active Member

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    Two
    Yep, exactly.

    If anyone else has kept track of this, I'm curious what sort of consistency we would see e.g. if ~5.5% difference is typical. I see people post frequently with a number they think represents the difference in their experience, but I'm not sure anyone has actually calculated it.
     
  4. Mendel Leisk

    Mendel Leisk Senior Member

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    Location:
    Greater Vancouver, British Columbia, Canada
    Vehicle:
    2010 Prius
    Model:
    Touring
    My error, pretty much from day one, is 7.21%
     
  5. FastForwardRay

    FastForwardRay New Member

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    Vehicle:
    2010 Prius
    Model:
    Four Touring
    This is great. I have not kept track of the difference but I always noticed a difference between what I calculated and what was displayed.

    I figured that the gas pump makes a difference, and there was some error in the software.

    I typically see 3-4 mpg difference.

    The difference is low when I have idled a lot. Maybe fuel usage measurements have an error at higher flow.
     
  6. Mendel Leisk

    Mendel Leisk Senior Member

    Joined:
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    Model:
    Touring
    If Toyota was a butcher they'd have a thumb on the scale. :rolleyes:
     
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