Prime Mileage Calculation

Discussion in 'Prime Fuel Economy & EV Range' started by DonJ, Jan 12, 2020.

  1. DonJ

    DonJ New Member

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    I just went through my first full tank using HV mode alone. My calculation, based on the amount gasoline to refill the previously full tank to full and actual miles driven indicates 55 mpg, while the Prime calculates 60 mpg. Is this typical?

    Thank you,
    Don
     
  2. bisco

    bisco cookie crumbler

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    sounds about right. long term average might be a little closer.

    was that the dealer filled tank?
     
  3. DonJ

    DonJ New Member

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    No, I have gone through several tanks of gas.
     
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  4. bisco

    bisco cookie crumbler

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    i have found over the years that every tank fluctuates a bit in regard to dash readout vs fill up calculation.

    perhaps the tank doesn't always fill up to the same point? idk
     
  5. Salamander_King

    Salamander_King Senior Member

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    For most Prius (not only PRIME but all of them), the displayed mpg is usually higher than calculated tank method number, if you do many comparisons, it will be average 5-7% difference. Over 2 years, I have filled my PRIME 54 times and had following discrepancy.

    max difference: +19. 96% (display mpg being higher)
    min difference: -1.92% (display mpg being lower)
    average difference: +5.59% (display mpg being higher)

    Your difference is +9.1% and it is higher than usual number but as @bisco said, over time it will average it down to 5-7%.
     
    #5 Salamander_King, Jan 14, 2020
    Last edited: Jan 14, 2020
  6. bisco

    bisco cookie crumbler

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    plus, it was an all hv tank, not sure if that affects anything
     
  7. Salamander_King

    Salamander_King Senior Member

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    For comparison of displayed MPG vs tank method calculated MPG purpose, pure HV mode or mixed HV and EV mode should not matter, unless the display limit has reached 199.9mpg for 2017 models. For models later than 2018, 999.9mpg for a full tank is virtually impossible to obtain. I have done many HV only full tank drive on my PRIME, and difference between displayed MPG vs tank method calculated MPG are just as variable as EV mixed tank.
     
    #7 Salamander_King, Jan 14, 2020
    Last edited: Jan 14, 2020
  8. Mendel Leisk

    Mendel Leisk Senior Member

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    You mean the discrepancy between calculated and displayed? Yeah that seems about the norm: Toyota likes to embellish the numbers. On my 3rd gen: 7.5% on average.
     
  9. jerrymildred

    jerrymildred Senior Member

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    Hmmm. Mine almost always says 199.9 mpg. Pump calculation is typically 250-400 mpg. LOL!

    But on long trips where I don't drive EV, it's usually 2-4 mpg optimistic.
     
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  10. Salamander_King

    Salamander_King Senior Member

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    OK... I edited my comment. :oops:

     
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  11. jerrymildred

    jerrymildred Senior Member

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    Gosh! I wasn't talking about you. I was just being goofy (as usual). :D

    But now that you've done it, that's a really good edit. (y)(y)(y)
     
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  12. Salamander_King

    Salamander_King Senior Member

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    Out of 54 fill-up in 2.5 years, I had 199.9 mpg displayed on the in-between-fill-up Tripmeter on the dash exactly once. On that tank, I drove 1752miles, total electricity charged 268kWh, total gas used 8.646gal, mpg displayed 199.9mpg, calculated mpg 202.6mpg. This is one of the very few samples that displayed mpg was less than calculated mpg.

    I am sure many 2017 PRIME owners have those incidents if they regularly drive on EV for longer than 1800 miles per tank.

    Now, I said this, I wonder if any 2018 and newer Prime owner has had 999.9mpg showing on the in-between-fill-up Tripmeter on the dash??? That would require at least 7500miles of pure EV drive in between fill-up, provided the fill-up takes at least 8 gal of gas.
     
    #12 Salamander_King, Jan 14, 2020
    Last edited: Jan 14, 2020
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  13. jerrymildred

    jerrymildred Senior Member

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    I've observed that our driving situations are at just about opposite ends of the spectrum. Your electricity is crazy expensive so you try to conserve it which gives impressive m/kWh, but reduces mpg. Mine is cheap so I use it as much as I can which helps mpg. And the higher speeds my commute has along with the stop & go, takes a big toll on my m/kWh AND mpg.

    I've had 19 fill ups so far since I got it last March. 15 were in May on the big road trip. The road trip tanks were 46-65 mpg; two of those trip tanks had near perfect indicated mpg (one just above and the other just below) and the rest indicated 2-4 high, as I mentioned. Non big-trip tanks ran from 1235-2615 miles with three of them being over 2,200 miles. If not for that trip, my first fill up would have probably been at about 3,500 miles, but the road trip cut that one short.

    Either way, this car still amazes me. If I was driving a typical 28 mpg gasser, I would have spent $966 more on gas over these miles as of Dec 27 when I last got gas than I have spent on gas AND electricity. By the end of today, I'll have over 1,000 miles on this tank and it's still over half full, so that savings number will take another big jump when I finally do get gas again and update the figures.
     
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  14. Salamander_King

    Salamander_King Senior Member

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    Yeah, our electric rate just went up $0.02/kWh starting Jan 1, 2020. It is now $0.21/kWh including all the tax and fees.:cry::cry::cry:
    Compared to the electricity, the gas price just went down $0.05/gal. Now standing at $2.40/gal.

    With EPA standard 25 miles of EV range and ~50mpg for HV, this means...

    For EV 50 miles distance with 6.5kWh for a full charge cost at ~4miles/kWh 6.5x0.021x2=$2.71
    For HV 50 miles distance will cost 1 gal of gas = $2.40

    However, I can get more realistic ~30 miles of EV range and ~60mpg for HV on average. But even with increased efficiency, I still get this...

    For EV 60 miles distance with 6.5kWh for a full charge cost at ~5miles/kWh 6.5x0.021x2=$2.71
    For HV 60 miles distance will cost 1 gal of gas = $2.40

    So with regular EV driving method, more I drive on EV mode, more it will cost to operate my PRIME.

    Now, with very EV conservative driving method I have been adapting to increase miles/kWh, I am getting more like 50 miles of EV range and 50mpg for HV. This means...

    For EV 50 miles distance with 6.5kWh for a full charge cost at ~8miles/kWh 6.5x0.021=$1.365
    For HV 50 miles distance will cost 1 gal of gas = $2.40

    Yap, I decreased my overall HV mpg from 60mpg to 50mpg, but now I can save overall operating cost by mixing EV drive within my HV drive.
     
    #14 Salamander_King, Jan 15, 2020
    Last edited: Jan 15, 2020
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