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Fuel Matters - Driving Range & Gas Tank Issues

Discussion in 'Gen 2 Prius Fuel Economy' started by cognoscenta, Jan 29, 2008.

  1. cognoscenta

    cognoscenta Junior Member

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    I am getting great mileage, but about 4 months ago (at about 10K miles on my 2007 Prius), I noticed that I was getting fewer miles per tank than before. I had been getting 410-425 miles without breaking a sweat. My mpg was even improving at 42 mpg.

    I won't go into the b.s. I got from the dealership when I went in to get this explained/fixed the first time, but today I called to find out about the fuel capacity of the tank and the fuel reserve that is left once the light starts flashing.

    I got a very helpful woman from the service department who told me that the gas tank is actually a bladder! This means that it collapses as it empties!

    Furthermore, IF YOU ALLOW THE TANK TO COMPLETELY EMPTY, IT FILLS WITH AIR AND WILL NOT COMPLETELY FILL WITH GAS AFTER THAT. This is undoubtedly what happened in my case. This is something that is still under warranty and can be fixed, and I have high hopes of this being done.

    I have a service appointment tomorrow, and I will let you know what happens. I thought you might be interested to know what no one else, to my knowledge, has noted: That indeed the gas tank should be filled before it reaches empty to maintain maximum fuel capacity.

    We might question the wisdom of putting a bladder tank in the car, but that's what's there, and there you have it.:rolleyes:
     
    #1 cognoscenta, Jan 29, 2008
  2. seasalsa

    seasalsa Active Member

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    "IF YOU ALLOW THE TANK TO COMPLETELY EMPTY, IT FILLS WITH AIR AND WILL NOT COMPLETELY FILL WITH GAS AFTER THAT"

    Interesting comment from the dealer, even if it is pure BS. There is a bladder in all North American Prius to limit emissions. It is sensitive to temperature and will not hold as much in cool weather as in hot weather. Try a few searches of this forum, it is a very common occurence. There is nothing that the dealer can do to fix it.
     
    #2 seasalsa, Jan 29, 2008
  3. cognoscenta

    cognoscenta Junior Member

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    So, it sounds like the service rep had an imperfect understanding of the fuel tank issue. I'm wondering then if the air bladder you're talking about affects the fuel tank/capacity at all. If it is a rigid tank, the bladder would have to be in the tank, or they would be unrelated!
     
    #3 cognoscenta, Jan 29, 2008
  4. JimN

    JimN Let the games begin!

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    Please search for all the posts ad nauseum about this subject. There is a flexible bladder inside the tank. It is there to reduce evaporative emissions. The volume is variable. Nobody is going to get a set range on a "tank" of gas. The gauges on all cars are inaccurate. Buy gas by the time the last pip flashes and relax. Don't get your hopes up at the dealer.
     
    #4 JimN, Jan 29, 2008
  5. drees

    drees Senior Member

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    Which San Diego dealership told you this?

    FWIW, lifetime average on our Prius here in San Diego is just under 46 mpg, but it's gone down a bit with the cooler weather from what it used to be.
     
    #5 drees, Jan 31, 2008
  6. qbee42

    qbee42 My other car is a boat

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    This does bring up the interesting question of how any introduced air is vented from the bladder. Obviously the rigid tank is vented or there wouldn't be room for the bladder to expand and contract. How about the bladder? Does the charcoal vent line attach to the bladder? I haven't looked at the mechanics of this.

    Tom
     
    #6 qbee42, Jan 31, 2008
  7. patsparks

    patsparks An Aussie perspective

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    Yes it does. The tank outside the bladder is vented to atmosphere through a filter and vapour sensors.
     
    #7 patsparks, Jan 31, 2008
  8. qbee42

    qbee42 My other car is a boat

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    Okay, but how about inside the bladder. That's the OP's original question. If you get air inside the bladder, how does it get out, other than trying to suck it through the fuel pump?

    Tom
     
    #8 qbee42, Jan 31, 2008
  9. bbald123

    bbald123 Thermodynamics Law Enforcement

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    I find this very hard to believe since the bladder is vented to air through the evap system. A good discussion is here:

    http://www.autoshop101.com/forms/Hybrid13.pdf
     
    #9 bbald123, Feb 1, 2008
  10. qbee42

    qbee42 My other car is a boat

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    Great link. That PDF has a lot of good information. It shows a vent line from the top of the bladder to the secondary tank, which is then vented through the EVAP system. This should purge any trapped air from the bladder.

    Tom
     
    #10 qbee42, Feb 1, 2008
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