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Prius 09 Fuel Indicator Question

Discussion in 'Gen 2 Prius Fuel Economy' started by joeuser, May 16, 2009.

  1. joeuser

    joeuser Prius Junkie

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    Last night coming back from work, my fuel indicator just turned from 2 to 1 bar (or PIP) as I parked in front of my house. I've got 475 Miles on this tank so far. Weather is around low 70s in NY City so its been fairly decent.

    Last time when I got to this level (2 to 1 pip) I had 448~449 Miles on the tank and was just on my way to work and refueled before reaching when my pre-fueled odometer reading was at 469.9 Miles. WHen I refueled, I fueled up 9.265 Gallons of tank. I had a FE of 50.6 based on the number of miles driven and the amount of gas fueled up (MFD was showing FE of 51.5) and I'm sure I've done a lot better on this tank.

    I'm wondering how much will this last pip last me. I want to push it to 500 miles but am afraid that there may not be enough gas to pump me all the way to work on Monday (23 Miles).

    Any ideas?
     
  2. Paradox

    Paradox Prius Enthusiast / Moderator
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    I don't think you would have a problem making it to 500 miles if the bar just changed from 2 to 1 but it's just a number. You'd probably get 40 out of that last pip give or take if you dont change your driving style dramatically. I wouldn't chance running out of gas though just for a number to self impress myself, but that's just me...
     
  3. a priori

    a priori Canonus Curiosus

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    If you've read any of the Stickies in this Forum, you've found out that the gas gauge really is more of a "guess gauge." The reason is the bladder in the tank.

    You never really know exactly how much gas you have left, so you need to be cautious.

    One safe way to measure where you are at in terms of gas in the tank is to multiply the last fill-up quantity by the current MFD FE reading (assuming you reset it during the fill-up). In your case, you put in 9.265 gallons. If your current MFD reading is 51.5 MPG (as was the case at your previous fill-up), then you could expect to have 477 miles available from that fill-up (9.265 gal. x 51.5 MPG = 477 miles).

    Because you've reached 475 miles, that means you are, basically, at the same point you were when you last filled up the tank.

    A real danger is to assume that because you put in 9.265 gallons, you still have 11.8 - 9.265 left in the tank. The bladder makes such calculations and assumptions unreliable. I've never been able to put in more than 10.1 gallons -- even when the final pip was flashing.

    You can go ahead and push it at this point, but if that last pip starts flashing, I wouldn't waste any time trying to get to 500 miles. Go to the nearest gas station ASAP.
     
  4. john1701a

    john1701a Prius Guru

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    Why would anyone want to push it?

    Opportunities come up with friends & family. Last thing you want to do is have to stop for gas when it's inconvenient... or worse, have no where to stop available.

    Why isn't a range of 450 miles enough?
    .
     
  5. richard schumacher

    richard schumacher shortbus driver

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    Go for it! Life is all about taking risks for a good cause.
     
  6. dogfriend

    dogfriend Human - Animal Hybrid

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    You need to add a sarcasm smiley. I use this one: :madgrin:
     
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  7. JimN

    JimN Let the games begin!

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    Buy gas. Heroes don't get out of tight situations, they avoid them. Get stuck in tunnel traffic with a purple battery, the ICE cycling on & off, and a flashing pip and you'll experience a real thrill.
     
  8. Celtic Blue

    Celtic Blue New Member

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    When you get the flashing pip fill it up at your regular station. That's what we started doing after the initial several months of shakedown.
     
  9. patsparks

    patsparks An Aussie perspective

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    put fear to bed, buy fuel at your earliest convenience.
     
  10. efusco

    efusco Moderator Emeritus
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    The last 2nd to last pip drops off at 20% of the total tank capacity. So, in theory, you should have a total of about 3.8 gallons of fuel. Now, that's the theory. B/c of the bladder issue it may be significantly less, plus there is a certain amount of unusable fuel (~ 1/2 gallon) that is in a well for the fuel pump to help keep it cool.

    So, at a minimum I'd guess you have a 1.5 gallons of usable fuel until you run out. At 50mpg you should have about 75miles worth if you want to push your luck.

    I routinely fill up about 50 miles into my last pip or 5-20 miles into the flashing pip and have never, yet, run out of gas and I have 87k miles on my '04 Prius.

    There is some risk, and it's being reinforced here b/c we know of many annecdotes where people ran out of gas very soon after dropping to 1 pip. But, IMO, for most people the risk isn't huge. Fill up when convenient, but within a few miles after that last pip starts flashing for sure.
     
  11. joeuser

    joeuser Prius Junkie

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    Crap MY FE dropped, well just a bit!
    I dont get it. My average on the MFD went from 51.5 to 52.2 between fuelups so I was actually expecting the gas to last me a little longer than it did in my previous fuel up. However, I calculated the mileage (498 Miles on 10.106 gallons) and it dropped from 50.6 MPG to 49.3 MPG.

    But I should attribute this to several things: wind/rain/etc on my commutes as of late, usage of a/c, windshield defrozer, added weight in the trunk, many passengers, etc. In case you're not in NY, I'll fill you in. Past two weeks have been overcast and raining all the time. Only recently did the weather clear up (a bit). I'm going to be monitoring the MFD quite closely (so far on the 87 miles the average is still 52.2 MPG and dashboard indicates all pips in place).

    Hopefully I can bring it back over the 50 MPG mark once again (and do better than my best tank).
     
  12. 2009Prius

    2009Prius A Wimpy DIYer

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    I would trust the trend shown by the MFD. The apparent drop from the calculation is probably due to the bladder.
     
  13. nooaah

    nooaah New Member

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    Hahaha that happened to me a couple weeks ago with 2 pips left and I was sweating a little. That tunnel was steaming hot, too.
     
  14. Kenko74

    Kenko74 Junior Member

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    I thought I'd revisit this post since I now have 8K on my '09, and I've never been able to "use" more than 8.4 gallons between "full" and the "last blinking PIP." So I'm a little envious that you can get more than 400 miles on a "tank" of gas. I was wondering if there's a technical calibration the dealer could perform to my fuel gauge system? Simple math, if I'm always averaging 47-48MPG, seems like I ought to be able to drive more than 325 miles... Based on reading these posts, I've never taken it below the blinking PIP stage, but I sure don't get the range I'd like to.
     
  15. 2009Prius

    2009Prius A Wimpy DIYer

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    That's approximately the same amount of gas when I fill up. So I think your fuel gauge should be OK. :)
     
  16. ken1784

    ken1784 SuperMID designer

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    It is not a fuel gauge issue, but a bladder tank issue.
    A dealer technician can't solve the problem, but a warm weather can. :)

    Ken@Japan
     
  17. hill

    hill High Fiber Member

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    Even in a CA winter with morning temps in the 40's, I've gone as far as 30 miles with a blinking pip ... but not on purpose, rather the next gas station was farther away than I'd hoped. This is averaging mpg's in the mid 50's. I've never gone more than 20 miles via blinking pip since then, and normally refill as soon as it hits one solid pip. Still ... it's nice to know what the limits are.

    .
     
  18. Kenko74

    Kenko74 Junior Member

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    I have the same distance limits whether it's summer or winter. I'm used to it, but again, I'm envious of the folks that can go 450+ miles on their bladders. My last PIP starts blinking at only 325 miles, even though I average 47-48 MPG. Boohoo, it's just not fair :(