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3 Fill ups and notice computer MPG off negative 3-4MPG

Discussion in 'Gen 3 Prius Fuel Economy' started by ilovemymac, Jun 20, 2013.

  1. ilovemymac

    ilovemymac Member

    Joined:
    Mar 7, 2013
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    Location:
    Gardner, KS
    Vehicle:
    2010 Prius
    Model:
    V
    I thought i had read the Computer would make your MPG off to the positve so if it says 50 im actually getting about 46-47. However on my V im getting the other way. 3 fill ups now 1 of them going all the way to no pips on the screen and car saying 0 miles ( still only put 9.98 gal in).

    Anyway all 3 times the car reads 48-51. However when i calculate the miles driven and the gal i put in. Filling at the same gas station the last 2 times and going to 2 clicks i am getting 3.5-4MPG better then what the car says.

    Why would this be? Should i be worried my speedometer is off or something which is causing it show the wrong miles? the wheels are stock and tire size is stock for the 17IN.

    Thanks guys.
     
  2. eliteconcept

    eliteconcept 700 mile club, top tank mpg 69.5

    Joined:
    Aug 18, 2010
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    Location:
    Indiana
    Vehicle:
    2022 Prius Prime
    Model:
    Limited
    No worries. Over 38000 miles I find about a 5% error in computer and hand calculated mpg. At 50mpg computer this figures to 2.5 miles less when hand calculated. No worries, computers are not perfect
     
  3. ilovemymac

    ilovemymac Member

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    Location:
    Gardner, KS
    Vehicle:
    2010 Prius
    Model:
    V
    Ok good everyone had always said it is off the other way. So just wanted to make sure.
    Thanks again
     
  4. eliteconcept

    eliteconcept 700 mile club, top tank mpg 69.5

    Joined:
    Aug 18, 2010
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    Location:
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    Vehicle:
    2022 Prius Prime
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    Limited
    Id just continue to keep track and see how you trend, 3 fill ups is a small sample size
     
  5. prius_in_pa

    prius_in_pa Junior Member

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    Jun 26, 2013
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    Vehicle:
    2012 Prius
    Model:
    Three


    To calculate your MPG, the computer basically takes the distance you have traveled divided by the amount of gas went into the engine. The computer itself is super accurate when comes to doing the math. However, the sensors or the devices that measure gas volume and distance are not 100% accurate. In addition, I believe that outside temperature would affect the accuracy of gas volume measurements.
     
  6. FriarNurgle

    FriarNurgle Member

    Joined:
    Apr 17, 2013
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    Vehicle:
    2013 Prius
    Model:
    Two
    Just use Fuelly and don't sweat a few +/-MPG variance.
     
  7. alfon

    alfon Senior Member

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    Location:
    seaside, oregon
    Vehicle:
    2010 Prius
    Model:
    III
    Prius is off even more in cold winter months from my observations.