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Got more mileage than what the display says

Discussion in 'Gen 2 Prius Fuel Economy' started by calredd, May 27, 2008.

  1. calredd

    calredd New Member

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    I bought my new 08 prius about 3 weeks ago. I filled my tank abt 8 days back and then reset my consumption trip info in the LCD display as well as in the odometer trip A. I drove about 440 miles to date from the last fillup and the LCD display says the average was about 54.5 MPG for which is felt good. But when I went to fill my tank (a little early than the reserve warning), the tank became full after I filled in about 6.63 Gallons. So if I do the math, my real average is 440/6.63 = 66 MPG approx which is a lot more than whats on the LCD display ie 54.5. I am not at all worried but just curious as to why it happened. Is this a cause of concern or matter of another prius milestone ? Oh by the way, I love my car and its really great.
    Thanks
    Carl.
     
    #1 calredd, May 27, 2008
  2. qbee42

    qbee42 My other car is a boat

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    Don't bother with doing the math. There is no way for you to know how much fuel you actually used for that 440 miles. The design of the Prius fuel tank, at least for the U.S. models, is such that capacity varies dramatically from fill to fill. If you want the details, search this forum for "guess gauge" and "bladder". The short answer is that there is much variability in tank capacity, with factors being temperature, pump settings, phase of the moon, and sexual orientation. Well maybe not the last two, but you get the point. The only way manual calculations are useful is to do them over a large number of tanks. I wouldn't bother with anything less than ten tanks; the accuracy gets better as the error is distributed. For the short haul, just use the mileage displayed by the MFD. It will be within two mpg of being correct.

    Tom
     
    #2 qbee42, May 27, 2008
  3. Danny Hamilton

    Danny Hamilton Active Member

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    I'd guess that you probably used a bit bore than 8 gallons of gasoline, but that the pump then shut off after adding a bit less than 6.7 gallons. The 1.3 gallon difference between fuel used and fuel added would likely be due to differences in how full the tank was when the pump shut off, and variability in the capacity of the flexible bladder inside the tank that holds the fuel.
     
    #3 Danny Hamilton, May 27, 2008
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