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Replaced gas bladder mpg dropped 10 miles to a gallon

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by sullidj, Dec 20, 2014.

  1. sullidj

    sullidj Junior Member

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    Dealer replaced gas bladder end of Nov on my 08 (123k)after emission error code under Calif warranty-I am 2nd owner- have put 60k on car-averaged 50.2 mpg since purchase--MFD consistenly averages 49 mpg since bladder replacement-Manual mpg calculation (miles/gals purchased) comes in under 40-Dealer did troubleshot could find no answer-I have put 1000 miles on car since gas tank was replaced-using same oil-same tire pressure-same tires-everything seems the same-I have never had a 10 mpg drop in the four years i have driven the car???
     
  2. Patrick Wong

    Patrick Wong DIY Enthusiast

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    It would be highly unusual for actual fuel consumption to vary so greatly from the mpg reported by the MFD once sufficient miles have been logged to smooth out refueling variations from one tank to the next.

    Is there any possibility of error in your manual computations?
     
  3. bisco

    bisco cookie crumbler

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    does the car operate correctly, other than the mpg's?
     
  4. sullidj

    sullidj Junior Member

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    3 separate fillups all just under 40 mpg. I was thinking the bladder still needed to expand to full opening but after 3 tanks not sure that is fesible.

    car is running fine.
     
  5. Patrick Wong

    Patrick Wong DIY Enthusiast

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    The bladder capacity is irrelevant to mpg. It is relevant only to the driving range of your car on a tank of gas...

    Is it your practice to reset the MFD mpg gauge after refueling? If you don't reset the gauge then it will be showing mpg history for an extended period of time. That history may not be relevant to your current driving conditions in very cold weather.

    In cold winter weather it would be difficult to get much more than 40 mpg if you drive on short trips and have the cabin heater on at a reasonable temp.
     
  6. sullidj

    sullidj Junior Member

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    It is my understanding that MFD mpg is for most recent (current) driving, not a historical average mpg. How do you reset MFD guage after refueling?
     
    #6 sullidj, Dec 21, 2014
    Last edited: Dec 21, 2014
  7. bisco

    bisco cookie crumbler

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    the mfd is meaningless. what is important is the average of the 4 tanks prior to bladder change out compared to the 4 post bladder average. both measured by gas pumped and miles driven.
     
  8. sullidj

    sullidj Junior Member

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    I have kept manual calculations since purchased 50.2 mpg average, have never got under 40 since owned until bladder replacement.
     
  9. bisco

    bisco cookie crumbler

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    that's what i was afraid of. i fear they did more than change the bladder, and left you with a puzzle, wrapped in an enigma.merged.how's the 12 volt? sometimes they run it down when working on a car, and it's never the same after that.
     
  10. sullidj

    sullidj Junior Member

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    If MFD mpg is a Historical average which I never reset, that could be the answer. I thought MFD mpg was just the average for the current tank of gas?
     
  11. bisco

    bisco cookie crumbler

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    sometimes they reset on their own, sometimes they don't. but mfd mpg can't change your pump calculation, so can't be the problem.
     
  12. sullidj

    sullidj Junior Member

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    If bladder wan't fully enlarged when installed and gradually enlarged over fills up that could imply different fill levels 9 1/2, 10, 10 1/2, 11 gals???
     
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  13. fuzzy1

    fuzzy1 Senior Member

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    Gen3s (such as mine) require a manual reset.

    I though the Gen2s would reset when you filled up, but then they should also show wildly varying MPGs during the first few miles, settling down only after more distance. If your MFD is showing a consistent number even shortly after fillups, then it is not automatically resetting for the current tank.
     
  14. 69shovlhed

    69shovlhed Surly tree hugger

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    my '04 and '05 both reset with a fillup. the '06 doesn't. I would guess an '08 wouldn't reset?
     
  15. dolj

    dolj Senior Member

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    06 -> Gen II's only reset the distance automatically to zero at each fuel-up, but the consumption figure is the average since the last time it was manually reset. Prior Gen II's reset both consumption and distance travelled automatically at fuel-up. There is a RESET button on the bottom right of the Consumption screen.
     
  16. bisco

    bisco cookie crumbler

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    it doesn't matter how many gallons the bladder let's you put in. you drive x miles, you put in x gallons and you do the calculation. the bladder is the reason you do an average over many tanks. the only way the bladder could change your average is if it's expanding with each fill up, but eventually, it has to stop. if you deduct a gallon from each fill up, how much does your average come up? how many gallons did each fillip actually take? how many miles driven on each?
     
  17. sullidj

    sullidj Junior Member

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    I divide miles by gals purchased if the size of tank is enlarging each time i fill up my mpg would calculate less.
     
  18. bisco

    bisco cookie crumbler

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    yes. you can determine that now by looking at your fill ups.
     
  19. Mendel Leisk

    Mendel Leisk Senior Member

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    Yeah, that's what he's saying, the tank capacity expanding with each fill, and it's only a thousand miles since the swap, say two fill ups?
     
  20. bisco

    bisco cookie crumbler

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    he said 4 fill ups. without the numbers, it's impossible to know. but if that's the case, it can't go on forever.
     
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