Refueling at 10 gallon mark

Discussion in 'Gen 2 Prius Technical Discussion' started by zetapam, Dec 7, 2008.

  1. zetapam

    zetapam Junior Member

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    I am getting 44 miles to the gallon, my fuel gauge starts flashing after I have driven around 380 miles. By my calculations, I should still have around 3 gallons left in the tank or about 130 miles left before I run out of gas. Is it alright to wait until I have driven 440 miles (10 gallons) before filling up, or am I going to run out of gas one day? Also, what is the bladder that everyone keeps talking about?
     
  2. john1701a

    john1701a Prius Guru

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    Disregarding the refill warning could get you into trouble.

    The bladder is a device in the tank there to eliminate evaporative emissions. It will interfere with your "maximum" range, hence getting a warning sooner than you had anticipated.

    If you run out of gas and continue driving, it will likely shorten the life of the battery-pack.
    .
     
  3. qbee42

    qbee42 My other car is a boat

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    You are going to run out of gas. Even the big Toyota god in the sky knows not how much fuel a Prius contains, so if you try to calculate, you are going to get burned.

    Tom
     
  4. dogfriend

    dogfriend Human - Animal Hybrid

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    Do you feel lucky? Well do you, punk? :D



    I have never seen the flashing pip in 25000 miles of driving. I have never run out of fuel in 25000 miles of driving. I believe there is a very strong correlation between these two observations.
     
  5. sdtundra

    sdtundra Senior Member

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    In the 13,600 miles I've been driving my Prius to play it safe, I refill between 2-3 pips to avoid running out or pushing it to the limit.
     
  6. rwyckoff

    rwyckoff Phev's Plus Home Solar power1

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    I have been using 10 gallons/ fillup for 5 years now without running out of gas, Infact I used 11.1 last week, and 11.5 on several occasions. However, I fill my tank up to the top of the filler tube. This will give you at least 12.5 gallons in the tank (according to the guys who did the one tank hypermillage run of 109mpg, and over 1300 miles.) And yes, this will put more gas fumes in the air, and an ocasional splash out of the tank. My calculations, observing the millage and mpg figures calculated by the cars computer/sensors, and how much I put in the tank can vary as much as 1/2gallon/tank, this despite my being very consistent on how I fill the tank. Beware the bladder! Beware cold weather! Thanks-

    Ron
     
  7. john1701a

    john1701a Prius Guru

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    That would be unwise in the north.

    Capacity of the tank shrinks as the temperature drops, since the bladder is effected by the cold.
    .
     
  8. hill

    hill High Fiber Member

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    Wow, sorry to hear you did that. Continually filling into the filler tube causes fuel to run back into the charcoal canister ... effectivly voiding the warranty regarding that part of your emissions equipment. One of the ecu's logs this kind of data. Maybe the bright side is your warrany is already expired anyway? In CA, parts of the car that pertain to emisions are warranted out to 150,000 miles. Oh well. In the future, for those who haven't done this? Please Dont. There's never any reason to fill any more than 10 gallons, to be safe. I think I've only put 10 gallons in on one ocasion, since 2004. In fact, since 2004, my best tank (over 700 miles, reading 71.6 on the mfd) mileage ever was refueled to only to 9.5 gallons, and even then, the nozzle had clicked several times.
     
  9. morpheusx

    morpheusx Professor Chaos

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    by calculating and being unaware of the bladder is precisely why I ran out of gas on my second tank. When its below 40 degrees outside only count on their being no more then about 8 gallons in there to be safe in the winter, summer time 10 gallons would be fine.
     
  10. Syclone

    Syclone Member

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    I guess that there must be something that I'm missing here. How important is it to take a chance of running out of gas and endangering you, your passengers and those in the cars around you for the sake of playing "how low can I run the tank before needing to fill up" game?

    Because the Prius has a digital gauge, that doesn't mean that it's any more accurate than the analog gauges on conventional cars. Combine that with a fuel tank that has a temperature induced 10% variation in capacity makes for an exercise in futility.

    Generally speaking, I try to fill up when the gauge hits one pip. Occasionally, I let it go to a flashing pip if I'm less than 40 miles from my favorite gas station (BJ's Farmingdale, NY). Depending on outside temp, fillup amounts vary from 8.5 to 10.5 Gallons. The fuel ECU in the Prius doesn't show "miles to empty" for a reason. Given the variability within the system Toyota engineers had no reliable way to do it. How can you combine that with "seat of the pants" calculations and come up with anything that makes sense.

    Let's run a contest on PriusChat to name the Prius fuel fillup version of "Russian Roulette". Danny could award some sort of prize from the Chat Shop for the winner (determined by a vote from PriusChat members).
     
  11. liam51

    liam51 New Member

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    So, being new here, how about some solid advice. I should fill up when one or two pips remain on the fuel gauge to be safe? And if so, on average, how much should my tank take to fill it in warm temperatures at this reading? Sorry, but I havent driven this new Prius past 250 miles yet....?
     
  12. dogfriend

    dogfriend Human - Animal Hybrid

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    Yes, this is what I do. It has worked very well for me. Typically I will fill up with 2 pips remaining.
     
  13. Celtic Blue

    Celtic Blue New Member

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    Refilling when it drops to the last pip we get about 8 gallons usable capacity (stopping when the pump first kicks out on low fill rate.) That's borderline acceptable. A reliable ten gallon capacity (hot or cold) would be good.

    How many owners would actually choose to have the complicated and delicate bladder tank if a regular tank (with its greater capacity, more reliable indication and fill) was a no cost option?
     
  14. David Beale

    David Beale Senior Member

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    I too don't understand why so many MUST run the tank down as far as they can go. Is there some reason you avoid filling stations? I refill at 1/2 tank when driving around the city. On trips I refill when convenient, but NEVER below three pips.

    You or anybody else CAN NOT estimate the amount of fuel you have used or will use to fill the tank, at whatever number of pips on the gauge. At best your estimates are +or- 10%.

    The reason is simple:
    1. The fuel tank has a bladder inside that expands to the metal tank walls when refilled. It varies in stiffness, so in colder weather may not expand or contract all the way. The weight of the fuel is what expands it, NOT the pressure of refilling. So it's not much force.
    2. There is a "pocket" built into the tank wherein lies the fuel pickup and the fuel pump. You can't predict how much fuel will be in this part of the tank.
    3. Because the filling routine/process causes venting through the smallish vent tubes, especially when the tank gets mostly full (nossle clicks off), there can be a 4-5 litre variation in how much fuel you actually put into the tank, depending on how sensitive the nossle cutoff is, and how much you pump -after- the first cutoff.

    As mentioned above, DO NOT fully fill the tank so you see fuel in the filler tube. If you do there is no room for the fuel to expand as it warms up (it comes out of the ground at about 40-50 deg F). While this is less of a problem in the winter, it's still not a good thing to force fuel through the vapour recovery system of the car. The car monitors this system and can detect damage very quickly (or five hours after you shut the car off). The repairs can cost upwards of $1000, and if caused by "over fueling" it's yours to fund.
     
  15. Celtic Blue

    Celtic Blue New Member

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    David,

    Why do you want to waste more time in the filling station, especially in winter? I can't understand why anyone wants to double the frequency of stopping for gas by refilling at 1/2 tank. Another problem is that the more you cut into the range of the tank the fewer options you have for choosing when/where to stop on a trip and the more times you will be stuck buying gas in more expensive locations. (One could make the case that for personal security it is safer to reduce your time at the station, although that is not my reason.) And on trips knowing that gas will be 15-20 cents a gallon cheaper across a state line or in another city is a pretty good incentive to use an extra pip or two.

    Let's put it this way, if I was going to half tank fills, I would do it on the bottom half of the tank only, leaving the top half empty. That would cut the weight the car was hauling around slightly, improving mileage and performance (admittedly a very small increment.)

    At any rate, unless the car starts running out of gas before it hits one pip, I'll refill at 1 pip. So far I have not relied on the idiot light.

    With normal gas tanks and gauges I look up the capacity and after a few fills I have a pretty good idea of how much effective capacity I have at various indicated levels. When conditions allow I've pushed my tanks to find the margins, but always leaving a small reserve. I've never run out in half a million miles in my personal vehicles.

    If a gas tank doesn't have at least the same range as my bladder or stomach, then it is insufficient.
     
  16. SageBrush

    SageBrush Senior Member

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    The tank bladder makes fill-ups quite variable, and even more so in cold weather. The only useful thing to know is that running out of gas is a BAD idea. Don't play with possible battery damage; find a gas station soon (within 20 miles) of the last pip starting to blink.
     
  17. ronhowell

    ronhowell Active Member

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    I have had my 2008 model Prius since September, 2007, with now around 8600 miles on the ODO (I'm retired, so the miles don't add up as fast as they used to).

    When I first got the car, I initially did not reset the MPG figure on the Consumption screen thinking that I wanted to preserve the cumulative MPG figure as the miles rolled up. (The miles figure automatically resets with anything greater that 3 gallons of gas pumped). I soon abandoned that idea, and went to re-setting the consumption screen completely at each fill-up. (I keep the cumulative MPG via an Excel spreadsheet).

    When you do this, you can check your fuel consumed at any point from the Consumption screen by simply dividing the miles since fill-up by the MPG figure, both of which are quite accurate, from the way the Prius calculates them. (If your MPG figure is close to 50, this is an easy mental calculation ... simply double the Miles figure and shift the decimal point two spaces).

    Monitoring this together with the fuel pip reading should enable you to determine how much fuel you can pump aboard at the next fill-up at a minimum, since you have just burned that amount since filling the tank!

    The most fuel that I have ever put in the tank is 11.1 USG, and that admittedly after I had driven further with a flashing pip then I would have wished (I wanted to gas up at a Costco in Stockton on a trip to Oregon). I wouldn't advise this kind if delay, but as a result of my cumulative experience, I estimate the Prius has about 1.5 - 2.0 gallons of fuel left in the tank when the fuel gauge starts to blink. That implies that you have no more than 50 miles more of additional range, since not all of this fuel is usable.

    So my advice is not to panic as the fuel gauge starts to blink, you're not about to kill the car. But you had better be within 50 miles of a gas station, so you can fill up at the earliest opportunity.

    PS. Forget about shirting the decimal point ... just divide miles since fill-up by MPG!
     
  18. liam51

    liam51 New Member

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    Thanks Ron, and everybody for the Sage advice given to me. So far, I am reading 49.2 MPG at half a tank showing. I'm impressed so far!!!
     
  19. richard schumacher

    richard schumacher shortbus driver

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    Unless of course this time the bladder is colder and stiffer, and thus cannot hold as much as last time.
     
  20. 9G-man

    9G-man Senior Member

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    If you reset you odometer and consumption screen at each fill-up, it's easy to know how much fuel has been used since last fill-up.

    At any time, Miles driven / averge MPG = fuel used . that is how much will be required to refill the tank.

    When you have filled you tank with at least 10 gallons, you'll know when you burned 10 gallons by running the numbers.
    I always get at least 10 gallon in my tank, and drive 600 miles between fill-ups in the summer, and around 530 miles in the winter.
    Because I get about 60 MPG in summer 53-55 in the winter.

    Works everytime
     
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