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MPG Anomaly

Discussion in 'Gen 2 Prius Fuel Economy' started by mjones675692, Oct 16, 2007.

  1. mjones675692

    mjones675692 New Member

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    I bought my Prius last July and have consistently been getting between 50 and 53 MPG everytime I fill it up. However, for some reason back in August, I only got to 431 miles before needing to fill up which worked out to be 42.8 MPG??? I did not do any unusual driving, the weather was not drastically different and ever since I have returned to my normal ~53 MPG.

    The only thing I did different is that particular tank of gas came from a small town gas station south of St. Louis. Could it be possible that a bad tank of gas can affect the mileage that much? What was also weird is that the on-board computer was reading 52 MPG average. Any thoughts on why this would have happened?

    Thanks.
     
    #1 mjones675692, Oct 16, 2007
  2. PA Prius

    PA Prius Active Member

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    The bladder takes on a life of its own at times, e.g. my last two tanks. In the one the actual was 5 mpg higher than the MFD, and in the other it was 5 mpg lower. In the long run I've learned that the MFD runs 1 mpg higher than true actual.

    PA P
     
    #2 PA Prius, Oct 16, 2007
  3. mjones675692

    mjones675692 New Member

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    <div class='quotetop'>QUOTE(PA Prius @ Oct 16 2007, 12:34 PM) [snapback]526432[/snapback]</div>
    I would agree that the MFD does run about 1 MPG higher, that is probably about what I notice on average, but I still don't understand how one tank of gas was about 10 MPG lower than all my other ones.
     
    #3 mjones675692, Oct 16, 2007
  4. PA Prius

    PA Prius Active Member

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    <div class='quotetop'>QUOTE(Hybrid Lover @ Oct 16 2007, 02:11 PM) [snapback]526446[/snapback]</div>
    Was your tank before or after this higher than usual, not MFD, but when dividing miles by gallons. This was the case in my example.

    PA P
     
    #4 PA Prius, Oct 16, 2007
  5. PriusRos

    PriusRos A Fairly Senior Member - 2016 Prius Owner

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    <div class='quotetop'>QUOTE(PA Prius @ Oct 16 2007, 02:20 PM) [snapback]526453[/snapback]</div>
    Do you reset your MFD when you fill up? (If you don't, it's showing the cumulative average, not the tank average, and won't change much).

    Also, could it be that you didn't completely fill your tank the time before, thus having to fill sooner the next time?
     
    #5 PriusRos, Oct 16, 2007
  6. donee

    donee New Member

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    Hi H.L.,

    A few things come to mind. Stuck rear brake, or rear brake operating technique specific to that tank, OR you got E85 for that tank. Driving allot of stop-and-go in the sun would do it too, but you said that did not happen (same driving and weather before and since).

    My guess is somebody slipped you some E85, or E50 or some such (put the E85 in a half full underground tank of E10).
     
    #6 donee, Oct 16, 2007
  7. mjones675692

    mjones675692 New Member

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    <div class='quotetop'>QUOTE(donee @ Oct 16 2007, 06:56 PM) [snapback]526603[/snapback]</div>
    I think I have to go with the reasoning that it was the gas. It was kind of a shady gas station. I was wondering if the bad gas could trick the MFD into thinking it got better gas mileage and maybe that would explain why there was such a discrepancy from the actual MPG. I don't know exactly how the MFD calculates the MPG, though.

    Thanks for all the thoughts.
     
    #7 mjones675692, Oct 16, 2007
  8. barbaram

    barbaram Active Member

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    Yes- too many variables.
    could be the station scammed you- pump not zeroed out ... maybe they had ethanol added which will affect your mileage. over the long haul it will average out... I never get too excited about any one tank, just look at the big picture :D
     
    #8 barbaram, Oct 23, 2007
  9. donee

    donee New Member

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    Hi HybridLover,

    The MFD measures the gas used, by the number of pulses and width of the pulses of injector squirts. And gets mileage from the odometer. Then it just divides the two. If you get bad gas, the car takes longer to accellerate, which is more squirts of longer duration.
     
    #9 donee, Oct 24, 2007
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