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MPG... Just mentally reduce what's displayed by 10%?

Discussion in 'Gen 4 Prius Fuel Economy' started by dslomer64, Jan 8, 2017.

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  1. dslomer64

    dslomer64 Member

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    For ten years, I developed the habit of reducing the displayed MPG in my Gen 2 by 10%. I find that with my first fill-up of my new Gen 4 that this apparently hasn't changed.

    Did I really expect the displayed MPG to be close to actual?

    No.

    I think I heard in 2006 that the estimate is made via an algorithm. If so, IT ISN'T CORRECT. CHANGE IT. Unless I'm missing something. Like what? In which case...

    Does anybody out there actually get the MPG displayed? How?



    Gen 2 (2006) and Gen 4 (2017)
     
    #1 dslomer64, Jan 8, 2017
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  2. krmcg

    krmcg Lowered Blizzard Pearl Beauty

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    Mine is a consistent 5% optimistic. So was my Gen 2
     
    #2 krmcg, Jan 8, 2017
  3. alanclarkeau

    alanclarkeau Senior Member

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    Mine varies wildly - I've had 7%, 2½%, 11% and 5% on my last 4 fills - all optimistic, though the 11% was by far the highest I've ever seen - they're generally around 4-5%. My 2 previous FORDs were optimistic too, but more consistently about 2-3%?
     
    #3 alanclarkeau, Jan 8, 2017
  4. bat4255

    bat4255 2017 Prius v #2 and 2008 Gen II #2

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    Sounds like my motorcycle speedo, 10% off.

    I just mentally adjust.
     
    #4 bat4255, Jan 8, 2017
  5. alanclarkeau

    alanclarkeau Senior Member

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    Yes - the speedo is 2km/hr optimistic no matter what speed you're doing up to 110 (which is as fast as I'm allowed to go).

    That works out at approx 2% optimistic at 100km/hr, 3% at 60km/hr, 5% at 40km/hr.

    Which could affect the l/100km/MPG figure - if driving at 40km/hr vs at 110km/hr - it could warp the fuel use figure?
     
    #5 alanclarkeau, Jan 8, 2017
  6. bisco

    bisco cookie crumbler

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    how do you know the pump is right and the prius is wrong.:sneaky:
     
    #6 bisco, Jan 8, 2017
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  7. alanclarkeau

    alanclarkeau Senior Member

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    I understand that they are monitored fairly well these days by National Measurement Institute (in Australia), and must be within +/- 0.3%.
     
    #7 alanclarkeau, Jan 8, 2017
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  8. bisco

    bisco cookie crumbler

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    with our new admin, i expect the pumps will deliver half of what is stated.:whistle:
     
    #8 bisco, Jan 8, 2017
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  9. Mendel Leisk

    Mendel Leisk EGR Fanatic

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    My my 3rd gen, tank-to-tank it jumps around some, always optimistic, and seems to have settled in on ~7.5% error.
     
    #9 Mendel Leisk, Jan 8, 2017
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  10. Prodigyplace

    Prodigyplace 2025 Camry XLE FWD

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    I have just compared my MPG once so far and the displayed alue was about 10% higher than actual.
     
    #10 Prodigyplace, Jan 9, 2017
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  11. dslomer64

    dslomer64 Member

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    What's even more puzzling is why MPG is reported to TENTHS of an MPG. IT'S NOT EVEN ACCURATE TO NEAREST ***FIVE*** MPG. (Okay. Maybe it's that accurate. Maybe.)

    I don't get it. With all the options, why not add an optional in-line gasoline-used meter and give MPG to nearest WHOLE MPG, guaranteed accurate since based on two measured quantities (or is odometer based on an algorithm?). MPG is main selling point, why not get it right?

    Gen 2 (2006) and Gen 4 (2017)
     
    #11 dslomer64, Jan 9, 2017
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  12. Prodigyplace

    Prodigyplace 2025 Camry XLE FWD

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    If you want to see something even more inaccurate, look at DTE (distance to empty). I think it always assumes you run the tank dry before refilling. Just top it up and watch it assume the distance between fillings was a full tank, not what was just added.
     
    #12 Prodigyplace, Jan 9, 2017
  13. Mendel Leisk

    Mendel Leisk EGR Fanatic

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    Just picture Toyota as a compulsive liar. They can't help but exaggerate, they've been doing it for donkey's years.
     
    #13 Mendel Leisk, Jan 9, 2017
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  14. bisco

    bisco cookie crumbler

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    think of all the happy souls who don't know the gauge is wrong. why would you want to break their hearts? toyota is brightening their day!(y)
     
    #14 bisco, Jan 9, 2017
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  15. Mendel Leisk

    Mendel Leisk EGR Fanatic

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    Yeah, that and the myth of Santa Claus. Oops, done it again.
     
    #15 Mendel Leisk, Jan 9, 2017
  16. greenmonster01

    greenmonster01 Member

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    I've only got 4 fillups, but mines about 7% higher than manual calculation.

    On a quick read, I just subtract 5mpg off of the MFD number.
     
    #16 greenmonster01, Jan 10, 2017
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  17. Mendel Leisk

    Mendel Leisk EGR Fanatic

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    IIRC Wayne Gerdes (CleanMPG) test drove a 2016 mule, and the mpg displayed was pretty much spot-on. This was an early produced vehicle, had signs of being hand produced, and was destined to be crushed (sob). I'm pretty much convinced the optimistic mpg display is a deliberate tweak.
     
    #17 Mendel Leisk, Jan 10, 2017
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  18. RCO

    RCO Senior Member

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    What bugs me is that you'd have to be totally retentive to need to calculate the difference over a month/ year/ lifetime! (n)(n)(n):whistle:
     
    #18 RCO, Jan 12, 2017
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  19. krmcg

    krmcg Lowered Blizzard Pearl Beauty

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    It is fun to do!
     
    #19 krmcg, Jan 12, 2017
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  20. Prodigyplace

    Prodigyplace 2025 Camry XLE FWD

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    Bored, are we?
    He obviously does not have a SWMBO. :D
     
    #20 Prodigyplace, Jan 12, 2017
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