How much gas are you able to pump into Gen3 when empty?

Discussion in 'Gen 3 Prius Main Forum' started by iskoos, Dec 1, 2019 at 9:00 PM.

  1. iskoos

    iskoos Active Member

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    My record is 10.5 gallons and that is with driving about 30+ miles after the onboard computer said I had zero miles to go.

    Normally, I pump when the last pip starts blinking (car says about 20-30 miles to go) and I can put between 9.5 to 10 gallons.

    The other day, I did my first road trip (500 miles). Started with a full tank and resetted the trip A. After driving about 420 miles (averaging 56 mpg), I was down to the last pip. And around 440 miles, it started lying again:rolleyes: "0 Miles to go". I wasn't going to pump fuel because it was technically impossible to ran out of gas at that point but it made me nervous and I made the stop after skipping a few exits. As you can guess, I was only able to pump 9 gallons (pump clicked before even reaching 8.5 gallons).

    It is of course a good thing to have some safety margin but I have never owned a car that has such an inaccurate fuel gauge. So annoying...
     
  2. spiralhelix

    spiralhelix Member

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    Well, tbh, according to people smarter than me, it isn’t advised to get the fuel that low as it makes the fuel pump work harder and wear out sooner.

    That being said, I pushed it (with a gallon can in the back just in case) to 11 gallons but don’t plan on ever doing again. My usual fill-up is 8-8.5 gal unless weather is a factor and it pushes it to 9 gal.


    -Spiral
     
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  3. fuzzy1

    fuzzy1 Senior Member

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    You aren't really going empty. Bob Wilson intentionally has, many times, for a variety of engineering tests. Here are just a few of them:

    [WARNING] Running out of gas (Gen III) | PriusChat
    My Gen3 Prius fuel gauges (2010, then 2012) are hands-down more consistent and linear than on any prior car I've ever driven. My Subaru is now a bit better, but it is also a newer design.

    All but one of those prior cars had very significant range beyond the fuel gauge 'E' or the low fuel warning light. One had a huge amount of fuel below that point. The single car lacking a large safety margin, actually went dry on me with the fuel gauge still above 'E'.
     
    #3 fuzzy1, Dec 1, 2019 at 9:14 PM
    Last edited: Dec 1, 2019 at 9:32 PM
  4. cnc97

    cnc97 Senior Member

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    I did 11.808 gallons last year when I did my 624 mile tank. That was 105 miles driven past the flashing pip. Even getting gas around the 0 miles to empty mark I average 8.9-9.4 gallons.
     
  5. Grit

    Grit Senior Member

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    11.9 us gallon when empty.
     
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  6. One4U2Envy

    One4U2Envy New Member

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    Since I have had my Prius 2010 Model my MPG has been at 44-45 City, 47-50 Hwy. Up until recently things have been really good then I had the new software update and I swear on the hwy I cant get over 38 MPG. I went back to the dealership and they told me nothing was wrong that I should drive in ECO mode more and so on. I have lost 70-80 MPG per each full tank of gas. Any advice on what the heck is going on?
     
  7. Maarten28

    Maarten28 Active Member

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    I've put that much fuel in once or twice.
    After the last bar starts blinking, I take 125 miles as maximum remaining distance and then fuel up usually around the 100 miles.
     
  8. Johnny Cakes

    Johnny Cakes Active Member

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    This subject often produces angry replies from people who swear that only idiots try to extend the range, but I think it is is an important topic. When travelling a long distance, fewer pit stops mean arriving sooner, or maybe there is really cheap gas at a truck stop xx miles away and you want to figure out if you can make it or should stop short instead, etc.

    One of my first threads was on this very topic: Summary of the Gazillion Fuel Left When Distance to Empty = 0 or Last Pip Flash and I got some "stupid topic" replies.

    But mostly I came away with:
    Not to high-jack this thread, but would anyone disagree with this statement:

    "IN AVERAGE/NORMAL FLAT HIGHWAY DRIVING, YOU CAN ALWAYS GO 50 MILES AFTER EITHER THE LAST PIP OR DTE = ZERO"
     
    #8 Johnny Cakes, Dec 2, 2019 at 5:48 PM
    Last edited: Dec 2, 2019 at 6:07 PM
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  9. iskoos

    iskoos Active Member

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    Haha, I get the humor but I tend to believe that you never past the 10 gallon mark.:)
     
  10. fuzzy1

    fuzzy1 Senior Member

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    Is this materially different than any other common cars? As in most drivers not usually using the last few gallons set aside as safety margin, regardless of make and model?
     
  11. iskoos

    iskoos Active Member

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    Thank you for being positive and supportive to my question. I was kind of guessing that I would get some negative answers but it seems most took my question seriously.

    And as for your question, That number should definitely depend on driving style and the MPG but I think 50 miles after DTE = 0 is 99% safe and I would endorse it (for Gen3 Prius).
    For me or drivers averaging 55 mpg or over, it should be well over 50 miles.

    On my last tank, I drove 65 miles after DTE = 0 point (with a 2 gallons of fuel in a fuel jug in my trunk. Just in case:)) and I pumped gas. I was expecting to reach to 11 gallons but the pump clicked right past the 10-gallon mark. I put some more but didn't even reach 10.5 gallons and I didn't want to push it.

    When I am in mood for my next trail, I will try 100 miles. This isn't to prove how much I can drive with a full tank of gas. It is to make sure how much the car is able to drive when I need it so I don't have to go through some unnecessary circumstances and leave a busy highway to pump gas while still having 3.5 gallons of fuel left in my tank. I was only 10 miles away from my destination.
    I understand that car manufacturers want to add a safety margin so people wouldn't get stranded in the middle of nowhere but keeping 100+ miles of reserve after the car screaming at you that you are on fumes is totally ridiculous...
     
  12. iskoos

    iskoos Active Member

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    I can't talk for all other cars but Gen3 Prius definitely stands out.
    I unintentionally drove to "0 miles to go warning" on another make/model car and I pumped 16.4gallons of fuel into the 16.5-gallon tank.
    I prefer this over what Toyota thinks is the norm...
     
  13. fuzzy1

    fuzzy1 Senior Member

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    For the cars I've been driving over the past four decades, this IS the norm. The exceptions were my very first car, which ran dry while still above E, and my first Subaru, which had nearly a third of its fuel tank below E. The others before Prius had roughly 100 miles of margin. Post-Prius, my newer Subaru has trimmed that margin to about 75 miles, but with more warning stages.
    100+ miles is totally ridiculous??? o_O

    Do you drive only where fuel stations are always close? I don't:

    [​IMG][​IMG]
    [​IMG][​IMG]
     
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  14. iskoos

    iskoos Active Member

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    Well I don't need to have 100+ mile safety margin so I can get to the next gas station in the middle of nowhere.
    There are gauges for that and if the gauges are correct and accurate and if we can read and interpret what they say, we should be able to know if making it to the next gas station is possible or not (even in the middle of a desert).
     
  15. fuzzy1

    fuzzy1 Senior Member

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    :LOL::ROFLMAO::LOL::ROFLMAO::LOL::ROFLMAO:
    The gauging certainty of fuel remaining until engine starvation has always seemed to be suspect.

    On top of that, the 'distance remaining' calculation is merely a forecast assuming the MPG of the route ahead will be the same as a certain distance behind. I.e. future results will be identical to past performance. But that is often not true, for reasons the car cannot know in advance. Out here in the mountains, and especially in winter, that assumption is often hugely separated from reality. Climbing multiple thousands of feet requires far more fuel than running flat. Changing weather often brings wind or liquid precipitation that significantly reduces MPG, and sometimes solid precipitation that can hugely cut MPG.

    I won't expect fulltime Florida residents to grasp the full extent of this elevation and weather MPG variability.
    Many people are not good at the mental math needed to figure an accurate answer, and are woefully unaware of just how widely MPG varies over different conditions. Thus, absent a significant safety margin, the Customer Service lines and representatives would get a flood of angry customers claiming, correctly, "Your car said I had enough fuel to get there, but then it stranded me out in the middle of nowhere, at night, in a storm!!!!"

    The best way to avoid those clueless but angry calls is to provide a substantial safety margin, more than enough so that customers know they have no one to blame but themselves.
     
    #15 fuzzy1, Dec 2, 2019 at 10:57 PM
    Last edited: Dec 2, 2019 at 11:27 PM
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  16. iskoos

    iskoos Active Member

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    Well, I understand "miles to go" greatly depends on the driving conditions. And yes mostly "Remaining miles to go" (what the car tells you) disappears much quicker than the actual miles driven. I always witness that. But this is an issue when there is a little fuel left in the tank. When the tank is full, estimations are more accurate. In my case for example, I generally go by how many miles my car can drive. I always reset my trip meter when I fill up. I know my driving style and where I drive. I have a ballpark figure in my head as to how many miles my car will drive me with a full tank of gas. And I always get that mileage.
    You can take my fuel gauge and MPG indicator and just leave me the trip odometer and I will not run out of gas (at where I drive).
    You take me to Washington, it will be a different story of course. But if I drive there a few weeks/months, I will develop the same for that region as well.

    What threw me off the other day was because it was the first time I did a long trip with this car. I went out of state. I wasn't in mountains but I also wasn't driving on flat Florida highways. When the car started screaming that I was running out of gas, I felt uncomfortable and had to pump gas which turned out that I absolutely didn't need it. I lost half an hour there for no reason.

    So in the end, it seems everybody thinks differently on this. It is better to be safe than sorry. I agree. But I am still thinking Toyota exaggerated this a bit too much. I would have been much happier if I could pump something like 11 gallons once the trip computer tells me "0 miles to go", Most people won't go that far and they will end up putting 10 gallons in and that should be fine.
    But now most people barely put over 8 gallons into 11.9-gallon tank. This is not okay to me. But I do know I won't be able to change anything. I am just venting...
    Desperatelyo_O
     
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  17. ASRDogman

    ASRDogman Senior Member

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    The one that is smart enough to open up a gas station half way to the next station,
    would probably make a lot of money. :)

     
  18. spiralhelix

    spiralhelix Member

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    Iskooi’s, I don’t disagree with your sentiment.

    On another forum there was a discussion about headlamps and using LED replacement from Amazon. Part of the discussion included that a lot of R&D is spent on headlights and the telemetry of the light from the projectors, blah blah blah. Do we know that for a fact? Do they just have to design something that reaches x distance when a tweak here or there would go 1/4 mile further??

    I guess what I’m trying to say, do we know if toyota pulled that reserve out of there nice person or did they have a legitimate rational behind it. Again from my other response, running low on fuel is said to make the fuel pump work hotter because it’s no longer submerged by a liquid that is acting as a cooling medium. So based on the dimensions of the tank, maybe toyota determined that those 3ish gallons is the safe level to maintain the pump. Can you go further, sure. /SHOULD/ you go further, not if you don’t want to potentially replace the fuel pump sooner.

    Additionally, (and I understand your 30 min out of the way issue) but over the life of the car, you are using the same amount of fuel regardless at which point you decide to pump. If I fill up every 1/2 tank instead of gauge empty, I’ll only put 4.25 gallons which takes less time to reach filling than the 8.5 gal (which from the moment I pull off the main road to pulling back on for me is 5 min). So maybe more frequent fill ups I would spend more time overall, but it might only be a 2 min difference per 11 gallons fill time that you spend.

    I hope that doesn’t come across negative, just a different viewpoint. Like I said, I did it once so I too would know if I could make it to that next station or not.


    (*side note, when I see a sign that says next station 90 miles and I’m close to E, I’m one that stops because there’s no guarantee that 90 mile station is still operational)


    -Spiral
     
  19. tallprius

    tallprius Junior Member

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    A risk of running out of gas often is that you will assist in the early death of your traction (the big one). Last year my weak 12v battery made gas gauge go nuts and I ran out of gas car - did not know it- and drove until car came to a total stop. That time my traction battery survived the no gas torture. One gallon of gas and car came back to life.

    Many episodes of running out of gas may damage your traction battery. In fact a big way to void the warranty on a traction battery is to have fault codes in ECU revealing you have ran car out of gas !
     
  20. Salamander_King

    Salamander_King Senior Member

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    I looked up my old record on my Gen3. The most I put in was 11.01 gal.
     
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