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Correct summary of the gazillion fuel left when "Distance to Empty = 0" & "Fuel PIP flash" threads?

Discussion in 'Gen 3 Prius Main Forum' started by Johnny Cakes, Dec 16, 2017.

  1. Johnny Cakes

    Johnny Cakes Senior Member

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    There are a gazillion threads regarding how much fuel is left when DTE says zero or when the last fuel PIP begins to flash and the audible alarm is heard. Many threads talk about how many MILES you can go, which is a pretty useless discussion since, literally, YMMV. Many threads devolved into "you are an idiot for not filling up when there are still x PIPs left."

    Anyway, I read all the threads until I got a headache and here's my summary -- does anyone agree/disagree?

    LAST FUEL PIP FLASHES:
    Bob Wilson seems to be the gold standard on this based on his actual testing. There are 2.1 gallons left when the last fuel PIP flashs.

    DISTANCE TO EMPTY REACHES ZERO:
    The consensus seems to be 1.8 gallons left.

    ACTUAL FUEL TANK CAPACITY:
    The tank is 11.9 gallons per Toyota. More gas can be added by filing to the top of the neck of the filler pipe, but the estimate for total capacity varied from 12.2 to 13.5. No real consensus. It seems like this is an important variable. For example,, when Bob Wilson says 2.1 gallons left, is just based on the official tank capacity or could there be more gas left if the owner filled beyond the tank itself.
     
  2. Mendel Leisk

    Mendel Leisk Senior Member

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    I've never been able to understand why any of this matters, maybe due to my spock-wired brain?
     
  3. jerrymildred

    jerrymildred Senior Member

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    Spock, if forced to estimate, would say something like, "There are approximately 2.09999335892129876 gallons left ... approximately." :ROFLMAO:
     
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  4. Mendel Leisk

    Mendel Leisk Senior Member

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    Puts me in mind, a very dedicated senior draftsman had just got himself a serious calculator, and was very impressed with accuracy, was not about to start rounding. There was a small plate needing to be welded in an inside corner of a wide flange beam, acting as a stop for a swinging arm. He worked out the angle of impact to the nth degree, and the checker kinda cracked up, it looked something like this:

    upload_2017-12-16_13-39-17.png
     
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  5. fuzzy1

    fuzzy1 Senior Member

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    While the full total capacity may be variable depending on how one tops off up that filler pipe, that variability should be relevant only to what is above the flashing pip and DTE=0.

    Bob's Gen3 out-of-fuel tests and fuel-remaining guidelines were strictly for what is below the flashing pip and DTE=0.

    Maybe also due to shorter trips, and your region's pattern of nearly flat fuel prices. No tourist trap, captive audience, or even 'convenience' price gouging where I've traveled. When I've been in Canada, there has been essentially no price incentive to wait until reaching cheaper gas ahead, except for when I'm headed back across the U.S. border*.

    (*) An exception was the east side of Glacier National Park**. Those northern Montana tourist zone prices were actually higher than in neighboring Alberta.

    (**) The U.S.'s Glacier N.P., contiguous with Canada's Waterton Lakes N.P.
    Canada has its own Glacier N.P. elsewhere.
     
    #5 fuzzy1, Dec 16, 2017
    Last edited: Dec 16, 2017
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  6. Johnny Cakes

    Johnny Cakes Senior Member

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    I just got home today from a trip up I-95 and this issue came up twice:

    1. I needed to figure the chance I can make it to South Carolina before re-fueling. The cost difference is five bucks for a fill up, which is more than all the hypermiling in the world could possibly achieve.

    2. The kids suddenly HAD to stop at the rest area (if you catch my drift). I'd like to delay the next stop as long as possible so that we don't run into that situation again, which is just a total waste of time.

    3. And it's just good to know -- e.g. I'm tired after work, do I really have to stop or will I have enough fuel to put it off to tomorrow.

    SPOCK OUT!
     
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  7. Mendel Leisk

    Mendel Leisk Senior Member

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    Yeah, I guess I treat the monetary side of it like buying mutual funds: just buy 'em on the 28th of each month, regardless of price, you win some, lose some, but in the long run it averages out.
     
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  8. bisco

    bisco cookie crumbler

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    i stop pumping at the first click (rounding of to nickel) and fill up when the pip starts flashing. it is always very close to 8 gallons (pip tank is smaller) and the difference makes the o/m spec for emergency fuel correct.
     
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  9. CR94

    CR94 Senior Member

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    The manual says 1.6 gallons left when the last segment starts blinking, so probably at least that much. Bob was probably right---for his sample.
    I quit paying any attention to the distance to empty gimmick when it showed zero before the blinking.
    Absolute capacity might be about 11.9+2+0.5, I'll estimate, but will not attempt to use it all.
     
  10. fuzzy1

    fuzzy1 Senior Member

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    14.4 gallons to the filler neck? That would be the highest claim I've seen yet. And not usable for those of us who don't want to mess with the vapor control system, or deal with warming fuel expansion overflows. Too much of that was involuntarily imposed on me on the farm.

    For those of us who stop at the first or second natural click of the gas station pumps, 11.9 gallons seems to be very close to the tank capacity to engine starvation.
     
  11. CR94

    CR94 Senior Member

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    Yes, I meant from very full to very empty. Absolute, not practical usable capacity. You don't need to worry about thermal expansion if you're about to burn off the potential excess before it warms.

    Our 1966 F100 was very bad about spurting gasoline out the filler cap on warm days even when well below full if it was leaning toward that side a little.
     
  12. Sam Spade

    Sam Spade Senior Member

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    THIS is the only "summary" that matters.

    The last word in OCD is "disorder". :rolleyes:
     
  13. wjtracy

    wjtracy Senior Member

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    My aged Gen2 is now getting only 6.5 gal fill-up from flashing. Sounds like from the noise in the pipe it is actually filling up. So the question would be if the flexible bladder has shrunk or maybe the flashing light is coming on earlier.