0 "miles to empty" = 50+ miles to go before running out...

Discussion in 'Gen 3 Prius Fuel Economy' started by aolm, Nov 29, 2017.

  1. aolm

    aolm Junior Member

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    The gas tank size is suppose to be 11.9 gallons. I just ran 5 or 10 miles past a 0 "miles to empty" indication then gassed up to "full" tank with 9.940 gallons (in NJ I did not personally fill the tank). Seems like I could have gone another 50+ miles searching for a gas station before running out. Is the tank absolutely 11.9 or is it made of a flexible material that changes? Has anyone ran out of gas and recorded the fill to full amount. I should get 11.9 x 48mpg=571 miles per tank... about.
     
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  2. CR94

    CR94 Senior Member

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    I would not take the "miles to empty" number too seriously. People who have measured say 2 to 2.5 gallons are actually left when the last gauge segment starts blinking (vs. 1.6 claimed by Toyota).
     
  3. fuzzy1

    fuzzy1 Senior Member

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    Bob Wilson has run out of gas many times, for fun / sport / engineering curiosity and testing. For a sample, including how much remaining fuel to possibly expect, read just the first post of this (much too long) thread:

    [WARNING] Running out of gas (Gen III) | PriusChat

    Note that he had a Liftback. Your 'v' will go fewer miles on the same fuel.
     
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  4. tvpierce

    tvpierce Senior Member

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    Miles to empty indicators are a gimmick. There are way too many variables for them to be accurate. It's like measuring thousandths of an inch with a yard stick.
     
  5. Mendel Leisk

    Mendel Leisk Obtuse Angler

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    Speaking of sticks, due to no gas gauge, my Dad would measure the remaining gas in our 58 VW bug's tank with a thin piece of cedar, dip into the tank, see how much came out wet.

    When you see, that the only thing between you and a long walk down the highway is an wet inch or so at the bottom of the stick, maybe you become more conservative.
     
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  6. fuzzy1

    fuzzy1 Senior Member

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    I would equate them more to weather forecasting based strictly on current conditions and recent and seasonal history at one's particular location, without any access to conditions elsewhere or weather radar or other tools to see what weather systems are moving in.

    Distance To Empty gauges cannot be highly accurate in variable real world conditions, but are still useful for the many folks who can't do long division in their heads. Reasonable allowance for variability is essential.

    Hey, much of my professional career in electrical Test & Measurement was based on this general concept. It most certainly can be done, with high accuracy yardsticks, zillions of properly dithered samples, and plenty of signal processing to distill the measurements.
     
  7. Maarten28

    Maarten28 Active Member

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    Gimmicks to such an extent that saying it is 0 when in fact you can drive another 50 miles (about one gallon) means that you can not measure the fuel level to any degree of accuracy.
    And that is just not true. When you read the fuel gauge via de OBDII port you get somewhat more intelligeble readings.
     
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  8. tvpierce

    tvpierce Senior Member

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    It's still just a rough estimate made using a crude instrument: a float in the tank manipulating a resistor.
     
  9. CR94

    CR94 Senior Member

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    Attached to a proper gauge, that's a lot more useful than the silly miles-to-empty gimmick.
     
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  10. fuzzy1

    fuzzy1 Senior Member

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    That depends on the driver's ability to do math in their head. Not everyone is good at long division without assistance.
     
  11. Grit

    Grit Senior Member

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    What if you were going uphill majority of the 50 miles and EV never gets the chance to kick in as it should, with wind and rain? I wouldn't follow that school of thought completely.
     
  12. Maarten28

    Maarten28 Active Member

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    In an irregularly shaped tank even.
    And what if he were going downhill the majority of the 50 miles and would be regenerating most of the time? But that's why a range to empty has so little use. The car can not think ahead, the driver can. When the car shows "1 gallon remaining", the driver can make a much more informed decision then when the car shows "0 km remaining".
     
  13. tvpierce

    tvpierce Senior Member

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    It wouldn't matter if Scangauge was capable of displaying thousandths of a gallon, it's still getting its data from the same place as the fuel gauge and the miles-to-empty display: a float manipulating a resistor -- a crude instrument that's designed to give a rough estimate of the amount of fuel in the tank. This is the same technology that's been measuring fuel level in cars for 50+ years. Just because it's connected to a digital display doesn't make it any more accurate.
     
  14. Maarten28

    Maarten28 Active Member

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    It is more accurate than a miles-to-empty indicator that goes to 0 when I can still drive 50-80 miles .
     
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  15. CR94

    CR94 Senior Member

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    Then they should do short division. It does not need to be very accurate to beat the miles to empty display.
     
  16. fuzzy1

    fuzzy1 Senior Member

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    Many can't do that either.
     
  17. Grit

    Grit Senior Member

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    DTE was 12 mi today, floored it going thru a yellow light at 35mph to 45 on ECO. YEEHAA!!! (Dukes of hazard)

    DTE immediately went down to 8 mi.
     
  18. CR94

    CR94 Senior Member

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    Probably for the same reason it drops after parking headed uphill.
     
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  19. Civiceg94

    Civiceg94 Member

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    Their was one night coming from work my dte said 4 miles. When i got home after driving 13 miles it still said 4 miles to dte. So i went to the gas station and filled up with 8.739 gallons in the manual says my plug in tank capacity is 10.9 i still had 2 gallons left which i find kinda annoying toyota didnt do this right should of done it like on every other normal vehicle
     
  20. fuzzy1

    fuzzy1 Senior Member

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    Considering the manner in which many drivers use this, without understanding how highly variable fuel consumption can be, it is imperative that car makers do something to flag drivers about impeding fuel starvation. Otherwise, Customer Support hotlines will be fielding a lot of angry calls from drivers who were stranded in adverse conditions, while legitimately claiming that 'the car said that it could drive my intended distance with the fuel it still had!'. Well, yes, it could under other & better conditions, but not under the adverse conditions of your specific trip.

    Toyota's approach is to set off a reserve 'safety margin' separate from the displayed DTE. My Subaru Forester gives a more accurate distance (but more coarse resolution,10 mile increments), but then gives three different low fuel warnings at different times, lastly completely blanking out the DTE display long before it would naturally reach zero.

    While I personally prefer the Subaru's approach, I'm not prepared to suggest that one is better for the overall consumer base than is another. But the makers may well be unable to exactly copy other maker's designs for legal intellectual property reasons, so must do something different.

    BTW, your PiP's DTE behaves different than those of normal Gen3 Liftbacks. In the later, DTE must drop at least 1 mile for every 2 miles driven, even when coasting downhill burning no fuel at all. When it shows 4 miles left, it cannot drive 13 miles and still show 4 miles left. It must fall to 0 within at most 8 miles. Because of the new all-electric capability, Toyota put different DTE programming into the PiP.
     
    #20 fuzzy1, Jan 6, 2018
    Last edited: Jan 6, 2018
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