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How low do you let your tank go?

Discussion in 'Gen 5 Prius Main Forum' started by priusmouse, Jan 6, 2024.

  1. priusmouse

    priusmouse Member

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    And is it bad for the prius to let its tank get too low? If so…how low is that?

    i’m interested purely from a mechanical perspective—does allowing the tank to get too low hurt the engine’s longevity?
     
    #1 priusmouse, Jan 6, 2024
    Last edited: Jan 6, 2024
  2. PriusCamper

    PriusCamper Senior Member

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    Fill it up and drive it till just before empty... If you want to get the best MPG possible, the more empty the tank, the lighter the car, the better the mpg.
     
  3. sclevine

    sclevine Active Member

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    I put almost 300,000 miles on my gen 4 and I'd almost always let it get to down to between 30 and 0 miles to go. Unless I knew I was in a dead zone or I knew I could save money at cheaper gas stations. It's not bad for the car. Even at 0 miles to go, I'm pretty sure there is still a good gallon left. My gen 5 is new so I don't have a ton of experience yet with it, but same thing. I fill up when it gets pretty close to 0 depending on my location and nearby gas stations.
     
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  4. ChapmanF

    ChapmanF Senior Member

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    It might depend on what all your objectives are.

    Are you chiefly interested in getting the absolute best MPG? Or minimizing how often you stop to fill?

    Or, do you live in a place where you might have some reason to unexpectedly want to get in the car and go because of some event? Could an event make finding a fill-up difficult on the way?

    Could you find your way blocked in inclement weather somewhere, and need to hunker in the car for a while waiting for unblockage?

    Do you have thoughts of using an inverter from your car to keep some things powered at home in a power outage? Or of using your car as a last-ditch heated/cooled place for you if your home heating/cooling conks out at an inopportune time?

    If any of those purposes might be relevant to you, you might want to pick some target level of the tank other than the very bottom, and try to keep the level at least there.
     
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  5. samsprius1

    samsprius1 HEV Fanatic

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    I let go down to below 10 miles to E! only took 8.4 gallons,,I think Limited has smallest Tank!!
     
  6. PriusCamper

    PriusCamper Senior Member

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    That's a very thorough answer that they probably didn't deserve, but good on you for making the extra effort.

    This Gen5 forum reminds me of the good old days when we had so many brand new Gen3 owners with lots of silly new car owner questions. Very nostalgic!

    Only two threads still missing that I haven't seen yet on here are "Oh my god I got a scratch on my paint, what do I do?" and "Oh no, I spilled my soda in my new car, how do I clean it up?"

    It's always fun to read about the terrible tragedies and horrific challenges of people who can afford to buy brand new cars that lose 1/3rd of their value in just a couple-few years. I feel so sorry for how hard their lives must be.

    I especially feel for the ones who carry multiple upside down car loans that don't get paid off before they finance their next car. It's not fair that they treat themselves so terribly...
     
    #6 PriusCamper, Jan 6, 2024
    Last edited: Jan 6, 2024
  7. bisco

    bisco cookie crumbler

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    when you get to zero dte, there's still plenny of gas in the tank
     
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  8. fuzzy1

    fuzzy1 Senior Member

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    I'm seeing a larger spec:
    [​IMG]

    So you should have around two more gallons left, a safety margin.

    How are you determining miles to E? If using Distance To Empty, many of us on an older generation have commonly found a couple gallons left, a bit more than our Owner's Manuals declared. (I don't see any equivalent statement in the 2023 manual). I've gone 60 miles beyond DTE=0 before 'wimping out' and refilling. Those who intentionally drove to fuel starvation, for testing purposes, have exceeded 100 miles. But these distance are also under excellent MPG conditions, not average. And one needs a fueling plan for when it does go out. Not recommended for foul weather, tight schedules, essential arrival times, lack of backup fuel, or nearly all other situations.
     
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  9. vvillovv

    vvillovv Senior Member

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    In summer I've gone 55 miles ( and 50 of those miles were at 60 and 70+ mph ) after the gas gauge read empty and the red light was on, several times and still had some gas left in the tank and at least 25 EV miles too. I did it once mid fall as temps were dropping, but I took a gal can with me just in case, and still had gas in the tank when I got there.
    In fall and winter I gas up between 1/4 and 1/2, and don't worry about it. A few years ago on one tank I made it from Buffalo to Fredericksburg, VA. I would have keep going to see if I could have made it to Richmond, but I got blowback on that idea from the passenger for at leas the last 50 miles.

    I wouldn't recommend anyone else trying to duplicate my results, unless they already know their car pretty well and or take safety measures if they want to push the boundaries, like some extra gas, just in case.

    I haven't noticed any ill effects from driving our Prius Prime down low on gas, but than again I wouldn't do the same in an older car, especially one without a sealed gas tank.

    @priusmouse are you near Captree? I used to take it to Democrat Point, Cedar or Gilgo to surf back in the day.
     
  10. fuzzy1

    fuzzy1 Senior Member

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    My spouse, driving home from a hike with a friend, and mis-remembering the fuel gauge rules I gave her, tried to apply my Gen3 Prius rule (~2 gallon safety margin past DTE=0) to the Subaru (NO safety margin, just more stages of advance warning). She was also getting passenger blowback, so finally relented and pulled over to get a spare couple gallons. Back-computing later, I'm surprised she hadn't already run out, my calculation indicated she was slightly lower than the time I deliberately ran it to fuel starvation as a test. With 10 more miles and a hill climb to go, she'd definitely have run out.

    From an old post:

    To paraphrase the low-fuel guidelines of another regular poster, more specific to the fickle fuel bladder of the GenII Prius:

    * With you mother-in-law in the car, fill up at 3 bars. She will never let you, or anyone else, forget that you stranded her.

    * With your wife in the car, fill up at 2 bars. She will never let you forget that you stranded her.

    * When alone, fill up at 1 bar. No one else needs to know that you got stranded.

    (While I do run my cars deep into low fuel range, to check their true ranges, the first forays are always carefully planned for benign situations where the cost of screwing up is minimal. In particular, no passengers to get upset.)
     
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  11. Sharol

    Sharol Member

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    When I had my first Prius in2001, there was a running joke on the discussion board that the Prius didn't have a gas gauge, but rather a guess gauge. The top half of the gauge had 8 gallons in it and the bottom half had 2. When that light started blinking, you had better be within sight of a gas station. I'm not sure when Toyota changed those. But the gen 1's were not particularly accurate.
     
  12. Hammersmith

    Hammersmith Senior Member

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    For the sake of fuel pump reliability, you should never go below 1/4 tank. That's real tank capacity, not necessarily 1/4 on the gauge. Considering there's a built-in reserve, I would say around 1/8 on the gauge.

    The reason is that the fuel pump generates heat while it's pumping. It's designed to be cooled by the surrounding fuel in the tank. If you drain the tank too much, there's not enough fuel to cool the pump and it overheats, shortening its lifespan. Regularly running the tank too low is the number one reason for fuel pump failures in Toyotas(other than recalls).

    It should also be considered that Toyota fuel pumps are built very well, which means they're more expensive to replace on average. Saving a few pennies here and there on very slightly improved mpg from weight savings could translate to many hundreds of dollars of parts and labor if you end up killing the fuel pump after <100k miles. (MSRP on the gen5 fuel pump is $544.16 + labor)

    It's the first one AMD talks about in his video on the five things you should never do to your modern car(2024 edition)



    1. Don't consistently run your fuel tank low
    2. Know what kind of engine you have(direct injection/port injection/both, turbo/non-turbo, hybrid/non-hybrid/plug-in hybrid)
    - make sure to push your engine("red-line it") at least a couple times a month to help blow out carbon deposits - esp. direct injection engines
    - avoid short trips at all costs; esp. in cold weather
    - be very careful with turbos; checking and changing oil is super important with them(doesn't apply to us Prius owners)
    - do not use long oil change intervals; 6month/5k mile/8k km for a healthy engine (even less for turbo engines)
    3. Don't hang things from places they're not meant to be hung from.
    - hanging something from your rear view mirror can get expensive if it eventually pulls the mirror and assorted wiring down
    - hanging something around your steering wheel/stalks can get expensive if it gets pulled into the spiral cable/clock spring and messes it up
    - even hanging something on your shifter can eventually cause problems(more so on standard automatics, not electronic shifters like ours)
    4. Whatever you do, don't use any glass cleaner with ammonia on your touch screens. It will ruin them instantly and be horrendously expensive to fix. (like over $12k for the gen5 Prius*)
    5. Don't let your car flood without a flood
    - sunroofs that open have gutter drains that can clog and flood a car(doesn't apply to us gen5 owners)
    - windshields(normally due to replacements); if it leaks, get it fixed immediately



    *don't believe me? Receiver Assy, Radio &amp; Navigation
     
  13. PriusCamper

    PriusCamper Senior Member

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    The Gen2 guess gauge was due to a rubber bladder inside the gas tank so when you filled up at the gas station there was no highly toxic air that had to be displaced to make room for the fuel. But it was the equivalent of putting a float-based water level meter inside a water balloon, which was why the gauge was so bad. Fortunately, they went back to traditional air filtering in regular metal tanks because of the hassle of the bladder not fully expanding in cars that rarely filled the tank all the way up that sometimes led to the bladder vomitting all over the person filling up the tank, which caused way more air pollution & personal health risks that the design was trying to avoid.
     
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  14. fuzzy1

    fuzzy1 Senior Member

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    Normally described as 'evaporative emission control'. I believe the EPA was concerned less about immediate fume toxicity, more about air pollution from photochemical smog. Evaporated hydrocarbons are one ingredient in the recipe for that smog.
     
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  15. HacksawMark

    HacksawMark Member

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    Why anyone would let their fuel tank get so low as to risk getting stranded is beyond me. Lately, I've seen more people walking on the side of the freeway with a small gas container in their hand either walking from or walking to their vehicle. What's even more strange to me is if they're walking from their vehicle with an empty gas container, I assume it's happened before, yet here they are again.
     
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  16. douglasjre

    douglasjre Senior Member

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    Usu takes 9.8-10.8gal to refill and it's 11.5gal tank (turd gen)
     
  17. fuzzy1

    fuzzy1 Senior Member

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    Some of us would like to have a better handle on fuel tank gauging, for when we cross long distances with no service or face adverse weather or other conditions. Or during an event where the clerk at the intended refuelling location is taking advantage of unusual circumstances in which he is the only station still open for a great distance, so demands a big surcharge to unlock the pump. BTDT. I walked in just behind someone else, and the gouging clerk may a point of saying they we couldn't split the surcharge. We both told him where to shove it, and walked out. That was in my long-ago first car with short fuel range, when fewer stations were available even during normal business hours, and in those days most closed on Sundays and major holidays, especially so when the two coincided.

    When unexpected or abnormal circumstances arise, knowing the real bottom of the tank, versus the 100+ mile range uncertainty from different gauging and safety margins in different cars, can be important when choosing whether to continue forward on the intended route, detour off the intended route, backtrack to the previous open station, given in and pay the clerk's ransom, or camp out at a closed station until it reopens.
     
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  18. Downrange

    Downrange Active Member

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    Thanks for goof info! Didn't know about pump cooling effect. I will say that in driving four Priuses since 2010, I've never run out of gas, and the time I really pushed it (drove a bit after "zero" miles left), it only took 10.1 gallons (2013 Prius 3). But, I don't like going below 1/8 tank since most fuel adulterants go to the bottom of the tank. Seems unwise, maybe clog a filter, burn some water?
     
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  19. vvillovv

    vvillovv Senior Member

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    Only having a Gen 1 for a weekend, end of Oct, I never noticed the fuel gauge issue. I did notice that fuel economy in late fall wasn't all that impressive and went with a Civic EX instead, which at the time got 35 city 40 hwy or 30 hwy if the dealer overfilled the oil. We didn't get into a hybrid until late summer 05.
     
  20. Sharol

    Sharol Member

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    My experience with my gen3 also. She was pretty amazing. When I sold her a year ago in late '23, I was getting 54 mpg according to the car and about the same figured on gas purchases. And this was at 11 years old (2012-IV).