Another gas gauge question

Discussion in 'Gen 2 Prius Main Forum' started by OC63RAG, Nov 19, 2021.

  1. OC63RAG

    OC63RAG Junior Member

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    I know there are tons of posts on the topic of gas gauges (and I've searched for an answer), but I haven't seen one addressing my question. Right now, I get about 350 miles out of a tank when I'm down to one pip on the gauge. I'm not comfortable running lower than that in case it runs totally dry.
    I'm getting 46 mpg on average and it takes about 7.2 gallons to fill up. 46 x 7.2 = 331 miles which is pretty accurate to what I'm experiencing.
    With all this in mind, is it safe to say I no longer have an 11.9 gallon tank but a 7+ gallon tank?
    I have no interest in driving around with 3 gallons of gas in a can inside the car in case I run out. If 350 miles +/- is my full tank distance I'll live with that.
     
  2. bisco

    bisco cookie crumbler

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    gen 2 has a rubber bladder in the tank that expands and contracts with the weather, or sometimes just contracts.

    you can try filling really slowly to see if it will take more. if not, the only solution is a new tank, if you want more range.
    there is a 2 gallon safety amount beyond the last pip, but i wouldn't trust it in the gen 2, they can be fussy.
     
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  3. mr_guy_mann

    mr_guy_mann Senior Member

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    Yep, live with it. The bladder inside a US spec Gen2 Prius is a "flexible" resin material. The idea is that the bladder can expand when full and collapse as it empties, which prevents vapors from forming because there isn't empty volume inside where the fuel is. Less vapor is good for less emissions overall.

    The problem is that as the car gets older, the bladder gets less flexible- esp in cold weather- so you can't fill it as much.

    Posted via the PriusChat mobile app.
     
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  4. ydpplqbd

    ydpplqbd Active Member

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    When you fill up try to fillup at the same pump each time. As the pump "clicks off" based on back pressure. With each pump requiring varying amounts of back pressure (IOW, there is no set standard for the back pressure threshold). Fueling at the same pump helps to create consistency in your fillups.

    Another tip: turn off your Gen2 when refueling. Apparently, turning car off helps to allow fuel bladder to relax and unfold. I do not know specifics but seems to work for me.

    My used Gen2 only took 6 or 7 gallons when I first purchased it used. Nowadays I regularly get between 8 and 10.5 gallons in the tank. This past spring, i intentionally ran my Gen2 out of gas in order to determine range. My range in that instance was 617 miles. Taking 10.9 gallons with air temp of 72F.
     
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  5. Tombukt2

    Tombukt2 Active Member

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    I get about 460 to flashing I add fuel to zeroed system and put 10.6 or so gal in tank ... Repeat 330K on car 10K changes since 200K. So boring I al.ost never check anything.cars been serviced like twice in life . Always consumables DOH!.. very similar to 2T and 7AF Corollas. All have made 500K always. Some never had headlight bulb

    SM-A715F ?
     
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  6. nemebean

    nemebean New Member

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    Is that all you did? My gen 2 that I bought end of August has never taken more than 8 gallons (with the last pip flashing) and now that it's getting colder it's been more like 7. It's not a huge deal, but it's kind of annoying to have to fill up every 250-300 miles. I already turn the car off when I fill up and I've tried filling it fast and slow, but it doesn't seem to make much difference.
     
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  7. OC63RAG

    OC63RAG Junior Member

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    I think I'm in the same situation as you. I'm guessing the bladder has become stiff/deformed and will only hold 7-8 gallons. Not the end of the world but it would be nice to get more distance out of a tank.
     
  8. Tombukt2

    Tombukt2 Active Member

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    Whoa bladder You mean like a well tank a pre-charged bladder inside the fuel tank that keeps pressure on the fuel That's weird when was an electric pump pump pumping to fuel injection I wouldn't think a bladder would make any difference in the tank but sounds good I've not looked at the schematic My 09 with 330 down to flashing lights and then adding 20 or 30 miles to that I feel up and I put 8.7 gallons in the thing shuts off but then I fill it at half speed right on up to 10.6 to 11.3 depending upon how hot or cold it is and fuel expansion and what have you In the dead of summer it'll be on the 10.6 side real cold in the winter 11.3 if I push it that 11.3 gallons will take me in the 460 range maybe a tad over and I'll be running into the gas station on fumes I'm pretty sure I've never checked but this is how I'm still gassing up yesterday I didn't know there was any bladders or any thing like that I do know that when it fills up and I keep filling it fast it'll gurgle and burp out of the tank but if I let it shut off first and then fill it like half speed I'll get on up there to almost full register tank which is what 12 something gallons 12 gallons.

    SM-A715F ?
     
  9. mr_guy_mann

    mr_guy_mann Senior Member

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    No, not precharged well tank. More like water balloon inside a box. The balloon expands and contracts as the amount of liquid changes. There's no "empty space" inside the bladder (balloon) so it can't create much vapor.
    When the bladder gets less flexible it can't expand fully.

    Posted via the PriusChat mobile app.
     
  10. ChapmanF

    ChapmanF Senior Member

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    Even when not aged, it's always more flexible in warmer temperatures, so the tank seems to take a smaller fill when it's freezing out.
     
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  11. ydpplqbd

    ydpplqbd Active Member

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    It is easier to get bladder to expand to factory specs in spring and summer (due to it being warmer). My method for expanding the bladder on my used Prius was the following:

    1. Always completely filling up each time at gas station for fuel.

    2. Keeping excellent track of average mpg, fuel pumped and miles traveled. Until you get your mpg number dialed in for the current season, you should use mpg average from last five fills.

    3. Refueling only when 25 miles past range. With range being computed as fuel gallons pumped multiplied by mpg. IOW, with the following hypothetical numbers: 7.2 gallons pumped with 48mpg average for last five fills works out to range of 345.6 miles. Under my system I would then refuel at 371 miles (345.6+25.0=370.6 >> say 371).

    4. Make sure that you have AAA Plus which provides "free" roadside service (namely, 3 or 4 gallons of fuel) if you should run out of fuel brought to you where you are stuck

    Worked for me. Let us all know how you make out. By driving 25 miles past range, you are consuming fuel in bladder that is not known to you, or your gauge ( a likely component of your problem). Additionally, by emptying the bladder as much as possible before refueling it appears to aid in stretching bladder towards factory specifications.
     
  12. ChapmanF

    ChapmanF Senior Member

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    I suspect a more sensitive test might be needed of whether that had the effect you think. The likelihood that further emptying an elastomer bladder somehow increases how far you can stretch it seems low.
     
  13. Tombukt2

    Tombukt2 Active Member

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    Mine ought to be stretched out like a war out you know what because I let that thing run down to fumes I know I do I know I've had it sputtering about to run out of gas pulling into the gas station

    SM-A715F ?
     
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