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Gallons used vs Gauge

Discussion in 'Gen 2 Prius Fuel Economy' started by PriusMikeAZ, Feb 8, 2008.

  1. PriusMikeAZ

    PriusMikeAZ Junior Member

    Joined:
    Jul 27, 2007
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    I drive the car until the last tick on the fuel gague blinks.

    I used to fill up and it would take a little over 10gallons. Now I fill up and it's taking 8.3 gallons or so.

    My computer says I'm getting 47 or 48mpg.. I figure it by hand it says 44 or 45mpg.

    What gives? I don't understand this bladder thing. What is the purpose of making a fuel tank that expands and contracts?

    Is this just a "winter" thing and in the summer I will have more "room" in my tank?

    Am I really using less fuel now? Is there something wrong with the fuel gague?

    2006 Prius
    13.000 Miles
    Phoenix, AZ
    - Mike
     
    #1 PriusMikeAZ, Feb 8, 2008
  2. qbee42

    qbee42 My other car is a boat

    Joined:
    Mar 2, 2006
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    Location:
    Northern Michigan
    Vehicle:
    2006 Prius
    This issue has been posted and commented on dozens of times. A quick search will give you a lot of reading material, but I'll recap it here:

    1) The bladder is there to reduce the amount of gas evaporating, which in turn helps keep down emissions.

    2) The amount it expands and contracts varies with temperature and other factors.

    3) The mileage on your MFD is accurate. What you calculate is not. Since you have no way of knowing how much fuel is really in your tank, you have no way of doing manual mileage calculations. You can do manual calculations if you do them over a LARGE number of tanks. That way the uncertainty of the bladder gets factored out.

    Tom
     
    #2 qbee42, Feb 8, 2008
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