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Fuel Capacity and MPG Calcs

Discussion in 'Gen 1 Prius Plug-in 2012-2015' started by Chicken Man, May 26, 2012.

  1. Chicken Man

    Chicken Man Brand-new to the Prius world

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    (I know there are similar threads, and I apologize if some feel that I'm needlessly starting a new one, but I didn't see anything similar in the PIP forum)

    I'm very new to the Prius world, and am having some significant difficulty reconciling the combination of fuel remaining in the tank and the car's calculation of MPG.

    Leaving work for my 30 mile mixed commute with 2 pips on the fuel gauge (had been 3 pips for my morning drive) and a full battery, the car started blinking with about 10 miles of driving remaining. The computer finally decided that that I only had 3 miles of driving remaining, however it stayed at that same 3 miles for about 4 miles of remaining driving before I could get fuel (Mind you I also had "4 miles" of EV capacity).

    When the car was filled, it took 8.5 gallons, which is 2.1 gallons LESS than the advertised 10.6 gallon capacity. The car computer stated that had 84 mpg for the trip/tank. My calculation was 74.5 mpg.

    While I fully understand the desire to not damage a fuel pump, or become a stranded hazard in the road, it seems like a 2+ gallon "idiot factory" is shortening my range by about 100 miles.

    Am I not understanding something about the fuel bladder system? Does my card need to be re-calibrated? Can I better (and precisely and accurately) hone this in with my ScanGauge II?
     
  2. bisco

    bisco cookie crumbler

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    hi chick!
    we all have a lot to learn about the pip. some things i know and some i'm guessing. others will jump in to add to or correct my thoughts.

    1) there is no bladder, hasn't been since 09 generation II. yes it's just the idiot warning system, but they want you to have plenty of warning because running out of gas in a prius can be a bit more troublesome than in a regular car. so when it starts blinking, it's best to fill up asap. you don't need recalibration, this is how the system works.

    2) the estimated range is just that. your actual range may differ depending on how you drive, the terrain and the weather including the climate system use. but when you get down to 1 mile of ev range, your close to empty (electric) and will be switching to hv (gas/electric)
    when you're total range is low, it's a bit more tricky because if you run out of gas, you're stuck. so again, best to fill up asap when the lite starts blinking.

    3) as for mpg's, i'm not positive, but i think the displayed is miles driven divided by gallons used and doesn't account for the boost you get from plugging in or the cost of the kwh used.

    4) feel free to ask me to explain any of the above, but i think i've confused myself. all the best! by the way, we just got back from your little burg out there and had a blast. beautiful weather, scenery, restaurants and people!
     
  3. fuzzy1

    fuzzy1 Senior Member

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    This shortened range due to the idiot light flashing roughly 100 miles before the tank is really empty is consistent with all but one of my current and past cars -- non-plugin Prius, and nonhybrids from Honda, Subaru, and Ford.

    My only outlier was an old Ford that ran dry with the fuel needle still above 'E'.
     
  4. john1701a

    john1701a Prius Guru

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    You drove over 600 miles before being told to refill. What benefit is there from driving further?
     
  5. Chicken Man

    Chicken Man Brand-new to the Prius world

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    WEEEELLLL . . . . Don't get me wrong, I love the car, and I love the ability to motor to baseball and tee-ball without burning any gas.

    The HUGE reason that I bought the car was for the CA HOV stickers--which are great.

    Before this PIP, my daily commuter was a 2003 VW Jetta TDI (diesel) wagon. That 9 year old car was able to go 600 miles before the fuel light came on. At 60-65mph (which is the frequent speed in the HOV lane) the diesel Jetta gets about 50 mpg--possibly/probably better than a Prius burning gas.

    Along with the decreased commute, and the electric driving, it would be nice to have a car that gets this "hyper-milage" and can give me a realistic vision of when I really need fuel, and possibly buys me more time between fill-ups.
     
  6. bisco

    bisco cookie crumbler

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    okay. but it is what it is.
     
  7. fuzzy1

    fuzzy1 Senior Member

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    That TDI had what, a 14.5 gallon tank? 50mpg * 14.5 gallons = 725 miles, not 600.

    How did you reconcile its difference between mpg, tank capacity, and fuel range any better than on your new PiP? It seems to me that it displayed about the same 'reserve' margin after the idiot light as your PiP and nearly all my cars of many makes listed in my earlier post.
     
  8. iRun26.2

    iRun26.2 New Member

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    But there is nothing wrong with complaining about the fact that nearly 2 gallons of the 10.6 gallon tank are not accessible. Is it not reasonable for the potential buyer to be able to accurately estimate how often they would have to bother filling up?

    It is what it is.., but why does it have to be the way it is?

    (I hate stopping for gas earlier than necessary on long trips too!)
     
  9. Chicken Man

    Chicken Man Brand-new to the Prius world

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    Fuel light generally came ON at +/-600 miles. If I got fuel RIGHT when it came on, it took 12.3 gallons.

    Part of the difference was, it was just a fuel LIGHT vs. a computer that implies that you're now operating your new vehicle in a reckless and responsible manner ?!

    They're both great cars . . . I guess I had a BIT of a different vision and hope that 9 years + some AWESOME hybrid/EV technology, I would maybe spend less time at the gas station?? . . .
     
  10. iRun26.2

    iRun26.2 New Member

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    The perceived need to 'idiot-proof' cars has not gone away. In fact, it's probably gotten worse: The consequences of running out of gas in your PHV and then possibly driving the traction battery until it's completely dead are far more serious (cost-wise, needing a new traction battery) than running out of gas used to be.
     
  11. fuzzy1

    fuzzy1 Senior Member

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    Thus, the TDI had a discrepancy similar to the PiP.
    ??? Doesn't the PiP let you just keep driving?
    Well, that would be true if the PiP had the same size fuel tank as the TDI, but it doesn't. Your boost in effective MPG is roughly the same ratio as the shrinkage of the fossil fuel tank, so I don't see where the expectation of significantly increased range came from.
     
  12. bisco

    bisco cookie crumbler

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    not sure what you mean inaccessable? are you saying the car will run out of gas with gas left in the tank?
     
  13. bisco

    bisco cookie crumbler

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    in my 08, the car would beep once very wuietly and the last gas bar would blink until you ran out of fuel. can anyone tell me what the pip does? i have only used 4 gallons in 5 weeks, so it's gonna be awhile before i find out. :)
     
  14. Chicken Man

    Chicken Man Brand-new to the Prius world

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    The experience (or "my experience") in the 2012 PIP is exactly the same. The beep seems very quiet, and the blinking icon doesn't necessarily draw a lot of attention given all of the other electronic feedback being processed.
     
  15. alfon

    alfon Senior Member

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    We currently have a 2003 Jetta TDI Wagon model GL with a 5 speed manual tranny.

    I have had few tanks of over 800 miles as the real tank capacity is at least 16 gallons
    of fuel and mpg was calculated at over 57 mpg, this is before the county went to
    low sulfer diesel fuel, the low sulfer fuel get 2-4 mpg less than the older
    fuel. Kind of what happened when we went to 10% ethanol in our gas.

    In comparison to our Prius the Jetta is about neck and neck on the highway
    with the Prius the clear winner during the summer. So far the prius
    for the last 1300 miles has been 53.8 mpg calculated, the Jetta about
    51 mpg....
     
  16. bisco

    bisco cookie crumbler

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    that's too bad. i ran out of gas in my 08 because i heard the beep one day and was planning to fill up the next day. of course, i forgot all about it the next day and never noticed the blinking pip again. i was hoping for something more obvious on the gen III.