Ran Out of Gas

Discussion in 'Gen 2 Prius Main Forum' started by TonyPSchaefer, Oct 14, 2006.

  1. TonyPSchaefer

    TonyPSchaefer Your Friendly Moderator
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    My last six tanks tanks all displayed higher than 60MPG on the MFD. But when I do the math, the mileage I calculate is sometimes way off from that the MFD showed. Here:
    Code:
    DATE         MFD            Calculated
    07/20        60.5            62.0
    08/02        61.7            53.3
    08/21        62.1            62.0
    09/14        63.1            71.8
    09/26        61.2            64.7
    10/13        60.8            51.2
    I'm fine to write off a slight difference due to gas station, temperature, and pump variations, but some of thes are outright crazy.

    So for this tank, I decided to refuel based purely on the math: averaging 61MPG I should have at least 610 miles in the tank. Right? NO!!
    The [Add Fuel] warning came up just past 500 miles and at 566.1 I got all the error lights and no ICE action.

    I assumed that I had run out of gas so I coasted into a parking lot and considered my options. After a brief pause, I figured that I might be able to make it to the closest gas station even if only on Battery. The really cool part was that when I powered up, the ICE came on. Apperantly, there was a little bit of gas still in the tank. So I limped to the closest station and filled up: 11.054 gallons. All the lights went off and I drove on. Happy ending.

    But I'm still confused about the displayed mileage versus the calcualted mileage. Who can explain that? For all tank info, click the link in my signature.

    Additionally, now that I'm aware of such great discrepencies, how do I portray it in my chart? I used to display both MPGs on the chart but stopped when they were always so close to each other. Should I bring them both back? Another alternative would be to "split the difference" and show an average of the two. That way, it wouldn't matter which one's higher.

    I'm open to thoughts.
     
  2. Bearcatzzz

    Bearcatzzz Junior Member

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    Out of curiousity, what did your gauge read?
     
  3. erogla

    erogla New Member

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    :lol: its not the gauge or the MFD, it is a defect in the nut behind the steering wheel !
     
  4. Beryl Octet

    Beryl Octet New Member

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    I think with the fuel bladder, the amount of gas you have when you fill up is not always the same, due to temperature difference and other variables such as the pump cutoff at the gas station. For example, I've filled up thinking I should be able to get at least 10 gallons in based on the MFD, but the pump cuts off after 9.2 or something and I can't squeeze any more gas in. Does that factor in?
     
  5. Prius Maximus

    Prius Maximus Senior Member

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    if you average out your mfd readings and compare them to the average of your calculated readings, they're only off by about a half mpg. I'm sure if you averaged all your readings and compared them they'd be closer. My calc vs. mfd mpgs agree to 0.05 mpg, although I also have individual readings that differ by 5 to 10 mpg.

    I believe it's the bladder, and how you fill it. I trust the mfd more than the calculted value.
     
  6. curtissac

    curtissac New Member

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    <div class='quotetop'>QUOTE(Prius Maximus @ Oct 14 2006, 09:34 AM) [snapback]332706[/snapback]</div>
    I agree. The first thing I did was average Tony's numbers. Shows that over the six readings, what the MFD showed and what Tony calculated differed by only .73 mpg.

    Tony: You have indeed fallen into the bladder trap. Probably the one "reliability" issue the Prius has. You cannot rely on the capacity of the bladder always being the same. It will vary some with every fill-up and that variance can be as much as a gallon - though more likely less than .5 gal.

    When you are getting 50-60 mpg or more, a variance of even one quart of gas will show the kind of differences you see in your calculated numbers. Average your calculations and the MFD calculations to prove it.

    I usually fill my Prius when the gauge gets down to four, maybe three pips (I think that's what people around here call the marks on the gauge). Somtimes I let it get down to two. I have seen my "range to two pips" vary by nearly 100 miles.

    Trust the gas gauge to tell when the car is low on gas. Though there are people that have reportedly gone from two pips to out of gas in short order so I wouldn't wait till one pip is flashing. Because of temperatures, pump shut off settings (which can differ at the same gas pump depending on delivery flow/pressure), maybe even even barometic pressure and a few other things, you cannot trust the gauge to tell you that bladder is really "full" (at its rated capacity).

    Trust the MFD to give you accurate gas mileage numbers, but remember that it is not using the bladder capacity to do the calculation.
     
  7. SiliconAddict

    SiliconAddict New Member

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    As a side question does anyone know how long I can reliably run when it hits one pip. Is even 10 miles questionable? 15? 20? There must be a safe answer. Sure I could fill it up now but I would like to see how many miles I can get on a single tank without being stupidly\dangerously low on gas.
     
  8. chimohio

    chimohio New Member

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    " Out of curiousity, what did your gauge read? " Do these things come with gauges?

    <div class='quotetop'>QUOTE(Curtis SAC @ Oct 14 2006, 11:27 AM) [snapback]332726[/snapback]</div>
    I usually fill up around 2 pips myself - I would estimate that about a 1/4 of a tank which is when I generally fill up in my other cars.
     
  9. hycamguy07

    hycamguy07 New Member

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    <div class='quotetop'>QUOTE(Beryl Octet @ Oct 14 2006, 10:27 AM) [snapback]332704[/snapback]</div>
    The 04's dont have this tank bladder problem that I know of, every fill up its 11.9 gal.
    I think its the math, (to many varibles) I always fill up at one pip thats 511 miles.(remember your mileage will vary due to your driving habbits) or when the one pip starts to blink I head for the closest gas station. As for the chart, the calculated numbers are bouncing at least 10miles etheir side of the mfd. (10 miles will make or break you in this car)! B)
     
  10. Bill Lumbergh

    Bill Lumbergh USAF Aircraft Maintainer

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    I don't get how people keep runnign out of gas. The low fuel warning comes on, the gas gauge last pip starts blinking, and people still don't get gas!

    Worry about how much gas the MFD thinks you should have after a fillup.

    I once ran out of gas in insane Friday traffic in Dallas, TX. I was stuck ni the left lane for so long I just ran out. I walked to a gas station and put 1 gallon in the only spare tank they had. I had to wait by the highway for 6 hours in the heat before the traffic was light enough for me to head for a gas station. I ended up stuck about thre hours south of home because my fuel pump burned up.

    Now I fill up with two bars left like clockwork.
     
  11. Charles Suitt

    Charles Suitt Senior Member

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    <_< Quote: "... The 04's dont have this tank bladder problem that I know of, every fill up its 11.9 gal. ..."

    My '04 varies a bit from tank to tank, but overall it calculates >98% accurate compared to manual calculation. I always fill at one non-blinking pip. I've *NEVER* been able to pump more than 10 gallons. I chose to *NOT* have the TSB done for "Fuel Gauge Inaccuracy" in early 2005 due to the extensive tear down/re-assembly procedure and reports that doing it only rarely made the "guess gauge" more accurate.
     
  12. hycamguy07

    hycamguy07 New Member

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    <div class='quotetop'>QUOTE(Boxster...WRX...Prius? @ Oct 14 2006, 01:35 PM) [snapback]332758[/snapback]</div>

    You know, this is the simplest idea to follow and you dont have to dammage anything pushing the car to its limits.

    Fill-up at 2 PiPs!
     
  13. Tony_Min

    Tony_Min New Member

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    You obviously have a terrible Prius. You average 60mpg, get 566 miles out of a tank. I would sell it if I were you. So far I haven't gotten more than 450 miles out of a tank, ran out of gas once at 422 and my average per tank has never been over 45 mpg. I pulse and glide until I get motion sickness, have my tires at 40/38. But yours, there is something wrong with it, I am sure...
     
  14. hycamguy07

    hycamguy07 New Member

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    <div class='quotetop'>QUOTE(Tony_Min @ Oct 14 2006, 04:20 PM) [snapback]332815[/snapback]</div>
    You know there are several factors that come into play regarding our MPGs.

    1. Terrain

    2. Weather/Temp

    3. Driving style/ road conditions

    4. city/hwy differences

    Maybe thats why the japanes did thier factoring ina more controled setting... I notice everyone tries to get better mileage & push the envelope. But in reality the car gets the best MPGs better than the other cars in its class...
    ;)
     
  15. Tony_Min

    Tony_Min New Member

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    Oh I know. I live in Northern California where there is no flat terrain. My car has only 1600 miles on it and I have been doing mostly short trips. Still, even taking those things out of the equation I wouldn't see getting much more than 50mpg.
     
  16. duanelaugh

    duanelaugh New Member

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    <div class='quotetop'>QUOTE(TonyPSchaefer @ Oct 14 2006, 09:30 AM) [snapback]332689[/snapback]</div>
     
  17. IsrAmeriPrius

    IsrAmeriPrius Progressive Member

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    <div class='quotetop'>QUOTE(Stan57 @ Oct 14 2006, 06:37 AM) [snapback]332692[/snapback]</div>
    Your question was answered in the original post:
    <div class='quotetop'>QUOTE(TonyPSchaefer @ Oct 14 2006, 06:30 AM) [snapback]332689[/snapback]</div>
    The Add Fuel warning show on the MFD when the last bar on the fuel gauge starts to blink.
     
  18. TonyPSchaefer

    TonyPSchaefer Your Friendly Moderator
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    The fuel gauge was blinking, the MFD was telling me to get gas. As I said, I first got the notice at around 500 miles and turned a blind eye.

    The defect behind the wheel acknowledges your compliment. :)

    I did not intentionally run out of gas but I was intentionally pushing my luck. This has nothing to do with attempting to maximize my MPG. Proof of that is the fact that I wanted to get gas a few days ago before the temps dropped to below freezing.

    As I said, it's the fact that the MFD was telling me that I was averaging 61 MPG and I knew that I had more than 10 gallons in the tank. It's not a far stretch to think that I should be able to travel 610 miles without needing to refill.

    Also, as I mentioned, I was getting eratic refill amounts in previous tanks when the gauge was telling me that it was time to refill. I mean, seriously, on the last tank that last pip was blinking and it took only 8.5 gallons.

    Therefore, I decided - intentionally - to disregard the gauge and drive for (MFD x 10) miles. And doing so caused me to run out of gas. Silly? yes. Expected? Sort of.

    To say that we should always trust the gas gauge because it always knows when it's time to refill means that we should disregard the MFD MPG. After all, they don't always agree. So which is it? Does the Prius know what your MPG is at all times or does the gas gauge know how much gas is in the tank? Clearly, it can't be both all the time.
     
  19. jkash

    jkash Member

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    <div class='quotetop'>QUOTE(Charles Suitt @ Oct 14 2006, 10:52 AM) [snapback]332765[/snapback]</div>
    I didn't have the Fuel Gauge Inaccuracy done on my 2004 for the same reason, but I have never come close to getting 10 gallons in the tank. I went all the way to the last bar blinking this week and was only able to put in 7.5 gallons. I can still get close to 400 miles on one tank, so I'm not complaining. The display read 54.9 and calculated was 53.3. I just passed 30,000 miles. I've recorded every fill-up. The average display is 53.65 mpg and the calculated is 52.54. The average amount of gas I've put in the car is 7.22 gallons.
     
  20. Skwyre7

    Skwyre7 What's the catch?

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    <div class='quotetop'>QUOTE(TonyPSchaefer @ Oct 14 2006, 07:37 PM) [snapback]332863[/snapback]</div>
    Ah, but it is both. The catch is, the Prius will only tell us one or the other. And it switches depending on it's mood. That is where the variability comes in. Sometimes it tells us the correct milage, hence the first pip disappearing after 150+ miles. Other times it tells us how much gas in the in tank, hence this thread. Or, it could be guessing at both an occasionally gets one or the other right. ;)