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How accurate is your Distance to Empty gauge?

Discussion in 'Gen III 2010+ Prius Fuel Economy' started by Glider, Jul 24, 2009.

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  1. Glider

    Glider New Member

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    I have 2 questions about the DTE (distance to empty) gauge which estimates "max dist achievable with remaining fuel"

    1) What does it mean? distance until engine conks out, gauge goes to 0 DTE, or single bar on gas gauge starts flashing?

    2) How accurate is it? When I last filled up (9.41 gal; 4th tank), it read 556 miles based on the last tank average of 55.5 mpg. Now, I've driven 355 mi and the gauge reads 160 mi DTE. That adds up to 515 mi. Where did the other 40 miles go? My ave mpg has stayed within 0.2 mpg of 55.5 during the whole tank.

    I am ecstatic to be getting around 500 miles/tank - don't get me wrong - just don't understand the variation considering the constant mpg I'm getting.

    Anyone have any ideas?
  2. CAR4TWO

    CAR4TWO New Member

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    Mine varries I've noticed. I can drive 25 miles and it drops from 533 at fillup down to 492 remaining so its all over the place.

    I filled up with 47 miles to empty and it only took 9.1 gallons to fill up and 11.9 gallon tank. So with 47 miles remaining at 1 pip, why do I have 2.8 gallons in the tank? I am going to get to the bottom of this so I can more accurately figure out when I need gas.

    I wished our cars had a fuel flow meter that told us the amount of gallons left in the tank. We get 50 miles to the gallon so it should be pretty easy to figure out when to fill it up with gas. A fuel flow meter is not expensive. I should find one and try to get it installed.
  3. Glider

    Glider New Member

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    I guess it is not too stable at the beginning, but it probably gets better when you are near 0 mi DTE. I've read that 0 DTE corresponds to 1.9-2.0 gal remaining, so your 47 DTE and 2.8 gal is right on the money. There is another thread about how much of that gas is actually usable, and the general answer is that it varies from tank to tank.

    The farthest down I've gone so far is 19 DTE, followed by a (heavy) 9.4 gal fill, which also agrees with your data. Assuming that I could have squeezed in another 0.2-0.3 gal, that also agrees with about 2 gal reserve at 0 DTE.
  4. DaveinOlyWA

    DaveinOlyWA 3rd Time was Solariffic!!

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    DTE is not extremely accurate. on my 622 mile tank i drove more than 70 miles past ZERO DTE. more than 120 miles on the last blinking bar...
    hybridbear likes this.
  5. Paradox

    Paradox Prius Enthusiast / Moderator Staff Member

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  6. bwilson4web

    bwilson4web 03 and 10 Prius

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    Huh? Did you drive to fuel exhaustion?

    Bob Wilson
  7. Glider

    Glider New Member

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    Thnaks for the heads-up. It's interesting that people are asking related, but different questions:

    - How accurate is the DTE? (this thread)
    - How accurate is the Fuel Gauge? (your link above)
    - When does the the ICE actually quit? (Bob Wilson's experiments)

    Since we don't know the detailed methods that Toyota uses to calculate the DTE or Fuel Gauge bars, it's hard to predict the answer to the third question. And there seems to be a large amount of variation (not yet cleat how much is random and how much is systematic) in the answer to the third question.

    I might run some experiments on the first two when I get time.
    hybridbear likes this.
  8. CAR4TWO

    CAR4TWO New Member

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    Bob, do you know what is unusable in the tank? Have you found anything in the owner's manual about that?

    Next time, I'm going to take it as close to zero miles remaining to see if that leaves me with about 1.9 gallons. The 2.8 gallons I had remaining at 47 miles to fill up is 23% of a full tank.

    In my airplane, 23% is one hour at full throttle. In my example above it would be about 100 miles at zero. How much of that is usable is the million-dollar question? It might depend on how level the car is when using that last gallon of gas.
    hybridbear likes this.
  9. fred garvin

    fred garvin New Member

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    when dte is zero, there are about 100 miles until you run out of gas

    as for variance in the dte calcs, what is the algorithm?

    (gas left - 2 gallons)/(?)

    (?) might be

    trip A or trip b mpgs calculated
    mpg of last X miles or gallons

    the latter is more accurate, in theory, because it assumes the mileage you just got will be close to mileage you are about to get
  10. DaveinOlyWA

    DaveinOlyWA 3rd Time was Solariffic!!

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    nope and i never do. filled up 10.334 gallons (real fill amount was probably a gallon more) and my "bush pilot/seat of the pants" calculation said i had at least another 50 miles i could drive before "becoming" concerned
  11. DaveinOlyWA

    DaveinOlyWA 3rd Time was Solariffic!!

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    one thing to consider that no one seems to....the gas gauge is not as bad as we think it is...its only "half as bad".

    the reason is when you determine that there is 2.8 gallons of gas in the tank, you might want to cut that calculation in half to keep from walking to the gas station.

    you cannot calculate your mileage based on you having a full tank. unless you dribble gas into the tank to the very top, you most likely had a full tank that is at least a gallon from being full.

    gas tanks have a vapor recovery cannister that is supposed to stay dry to be effective. so your tank, by design is set to shut the pump off in PLENTY OF TIME. now, the recovery tube and filler neck volume is not included the the specs for tank volume, but all systems have to have a designed safety margin and the vapor recovery cannister does play a rather important role in your car's operation.

    so, topping off the tank is ILLEGAL, (yep, read the warnings on the gas pump.) and unwise (can cause a very costly repair job as chronic overfilling results in replacing the filter and premature death of the fuel pump. a clogged filter causes back pressure in the system)

    i guess what we really should do is start a thread entitled

    What is a safe volume to add after the first shutoff ?(assuming the pump is working correctly)

    **edit** please ignore the thread suggestions... i dont want Toyota suing me when fuel system failures go beyond the MTF specs
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  12. wvgasguy

    wvgasguy New Member

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    I guess another question I would have is what makes up the 11.9 gallon capacity. If the filler tube part of that or is it just the tank.

    Maybe someone would syphon ALL the gas out ofntheir tank and then top it off and let us know?
  13. DaveinOlyWA

    DaveinOlyWA 3rd Time was Solariffic!!

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    nope. filler tube is not part of the stated tank volume and to be honest with ya, i am not sure that stating a tank volume is the greatest idea that Toyota had....

    i can see it in a 15 mpg work truck, but in a 50 mpg vehicle??? seems to cause more problems than its worth.

    granted a better gas gauge would be nice, but the closer to accurate it gets, the higher the # of people running out of gas...
  14. ctrlaltf

    ctrlaltf New Member

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    Recently,the fuel gauge indicated that I had 2 bars left of gas, yet distance to empty said 0. I added half a tank and it still read 0. what gives?!
  15. xs650

    xs650 Senior Member

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    There is a thread on Prius Chat started by Bob Wilson where he ran his Gen III dry a few times to find that out. The 11.9 rating is close to what he found out.
  16. Judas Prius

    Judas Prius Junior Member

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    I asked this same question about a week ago. My DTE was 55 miles. I filled up with only 8.6 gallons at 434 miles on the tank. So I still had 2.7 gallons left with one pip on the fuel gauge.
  17. oldasdust

    oldasdust Member

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    Who cares and why test fate?? Mother prius will spank you if she is allowed to run dry.
  18. alfon

    alfon Active Member

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    I have said this many times and this should be
    taken into consideraton:

    When you fillup your tank when the pump clicks
    off you can still nurse at least another 2 gallons
    into the tank to the top of the filler neck.

    This alone will give you another 90-110 mile range on a
    full tank.

    I know this is a no no for some of us and I understand, but
    if your talking range untill empty this probably should be
    considered.

    alfon
  19. Caug1

    Caug1 Member

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    My last feel up 11.333galons @ 585miles.
    i was worried.
    c
  20. vday

    vday Member

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    I believe you had 3.3 gallons left :)