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Fuel remaining - which gauge do I trust?

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by afob3, Aug 21, 2015.

  1. afob3

    afob3 Member

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    I've had this car for a couple of years now and I think this week is the first time I didn't 'fill up' when I got gas. I was in a hurry and just threw 10 bucks in the tank.

    So now the trip computer is all confused on miles to empty vs. the almost half tank I have on the fuel gauge. I've tried reseting the trip & holding the button to reset when miles to empty is displayed. I'm a little nervous with the miles to empty in the single digits now. Anybody else seen this before?

    IMG_0245.JPG IMG_0248.JPG
     
  2. FuelMiser

    FuelMiser Senior Member

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    With the Gen II, I was aware that you needed to add at least 4 gallons to register with the computer, but I was not aware of this restriction in the Gen III. I'd say you should ignore the "miles to empty" and rely on the pips on the fuel gauge, assuming 50 miles per pip, to determine when to fill up again.
     
  3. OBJ

    OBJ Member

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    I don't pay attention to "miles to empty", I trust the fuel gauge and the odometer.
     
  4. bisco

    bisco cookie crumbler

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    agree with the above, and fill up as soon as possible.
     
  5. afob3

    afob3 Member

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    I think fuel miser has it but hope somebody else can confirm. I filled up completely (6.5 gallons) and the miles to empty corrected itself within a 1/4 mile. I usually keep trip A showing and switch to the miles to go when I get to a quarter tank so I've never paid attention to it after adding fuel.
     
  6. Paradox

    Paradox Prius Enthusiast / Moderator
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    Unless you paid $1.54 a gallon, I don't think you added 6.5 gallons as you said you threw 10 bucks in the tank. I honestly think it is what Fuelmiser said as that was my first thought. I'd wait it out and do a half a tank or more fill up next time and see what happens.
     
  7. The Electric Me

    The Electric Me Go Speed Go!

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    Which gauge should you trust?

    Follow the "Scar Face" approach, who do I trust? I trust me!

    Listen, seems to me you added fuel. So even if it wasn't enough to register, it was an addition. Which would lead me to believe that if anything your distance to empty is being "pessimistic" , probably reading from the "lesser" pre-10 dollars added amount. So I'd guess you are pretty safe ignoring the distance to empty, and going more with the pips.

    Of course the easiest remedy at this point is to simply fill it up and reset at that point.

    But my speculation would be that in this case the pips are more accurate, and distance to empty is simply not taking into account the addition of fuel you added.

    My disclaimer and caveat here is that I'm speculating. If you're at all "nervous"...a fill up at any point will give you a full tank.

    I'd feel bad if your next post was about how you ignored the DTE and ran out of gas. Even though I think you're pretty safe.
     
  8. fuzzy1

    fuzzy1 Senior Member

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    Don't 'trust' any of them. But DTE is less meaningful than the pips on the fuel gauge, so put more faith in the fuel gauge.

    If you didn't put in enough fuel for the computer to be certain of an addition (as opposed to sloshing liquid level), and DTE didn't jump up, then DTE becomes absolutely worthless until the next fill. My experience is that it will continue to count down a minimum of at least 1 mile for every 2 miles driven. This is also true when gliding downhill for extended distances that burn little or no fuel. Without recognizing that added fuel, it cannot climb to reflect the new reality of an extra gallon or so, or vastly improved MPG conditions.

    This is completely different than the DTE behavior of my family's new Subaru, which rises and falls according to the most recent 30-ish miles of conditions.
     
  9. magnumrtawd

    magnumrtawd Member

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    HE never said he got 6.5 gallons for 10$
    Pay attention!
     
  10. afob3

    afob3 Member

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    It is interesting that it needs more than a few gallons to register a difference on the DTE. I learned something new from breaking my fill it every time habit.
     
  11. bisco

    bisco cookie crumbler

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    once you've owned it awhile, you'll have a much better feel for how far you can drive based on the gauge. the pip has 8 bars, and they are pretty close to a gallon each.
     
  12. Robert Holt

    Robert Holt Senior Member

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    Could also use a Scan Gauge II and calibrate its gallons-to-empty readout so that you have a second, digital, calibrated estimate of fuel remaining .

    I have noticed that the calibration shifts down a bit with summer blend or E0 gasoline, and up a bit with winter blend and E10 gasoline, so apparently you really do have to be aware of what kind of fuel you are using as well as how you are driving on a tank of gas.
     
  13. fuzzy1

    fuzzy1 Senior Member

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    I can't speak for your PiP, but regular Gen3 Liftbacks have 10 bars.

    On mine, bars 2 through 8 are pretty close to a gallon each. Number 1 never goes out (though the solid phase is about one-half gallon before the blinking phase starts), number 9 is short of a gallon, number 10 is long.
     
  14. macman408

    macman408 Electron Guidance Counselor

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    From the manual page talking about the Distance To Empty display:
    • When only a small amount of fuel is added to the tank, the display may not be updated.
    When the gauge shows you're low, fill up. Ignore the DTE until then.
     
  15. qdllc

    qdllc Senior Member

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    Lesson learned, fill to max.

    If you do a temp fill, I'd not let it go below 1/4 of the gauge before you put more in...just to be safe.
     
  16. CR94

    CR94 Senior Member

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    Such restrictions shouldn't be necessary. Partial fills when appropriate or unavoidable do no harm. Just ignore the car's distance to empty claim when it doesn't make sense.
     
    fuzzy1 likes this.