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Biggest difference between MFD and calculcated MPG

Discussion in 'Gen 2 Prius Fuel Economy' started by philwojo, Jul 6, 2006.

  1. philwojo

    philwojo Member

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    Not sure if this is the right place to post this but I will start it here, but feel free to move it if necessary.

    What is the biggest difference you guys have seen between the MFD MPG and your own Calculated MPG?

    I ask this because I know there is a slight difference, even up to 3-4 MPG sometimes, but I was on a trip all HWY miles over the 4th and for the tank it was almost 9 gallons.

    The MFD showed 49.3 MPG and I had reset it at the start of the tank.

    My calculated was 40.193857 MPG.

    That was calculated as follows:

    319.3 Miles / 7.944 gallons of gas put in to the tank.

    I never force any gas in, I just round to the nearst 1/4 of a dollar. It clicked at $23.33 so I took it to $23.50 and stopped, and that is how I do it every time.

    I'm not concerned all that much, more curious what is the biggest difference people have seen.

    My overall for about 3500 miles on the car between the MFD and Actuall are very close

    MFD = 51.15
    Actual = 51.0963

    thanks,
    Phil
     
    #1 philwojo, Jul 6, 2006
  2. narf

    narf Active Member

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    You probably know this but it's easy to get a partial fill of the tank, so sometimes the calculated mpg will be a bit off. I've had a tank where the calculated MPG was 10 MPG high. Of course was followed by a tank where the calculated MPG was 11 mpg low, so it averaged out. Over the last 9000 miles the average mpg display was 50.3, the average calculated mpg was 47.06, for an error 3.25 mpg or about 6.9 percent.
     
    #2 narf, Jul 6, 2006
  3. anewc2

    anewc2 New Member

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    I routinely get a difference of about 6-7% between the mileage shown with the trip A odometer (which I habitually reset with every new tank) and what I calculate from the fill-up (which is lower).
     
    #3 anewc2, Apr 19, 2011
  4. Bob Comer

    Bob Comer Active Member

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    I average a 8.4% difference between MFD and actual -- or almost 4mpg, since I bought the car 6 months ago.

    Calculated average since I bought it 45.619, MFD average 49.552.
     
    #4 Bob Comer, Apr 19, 2011
  5. qbee42

    qbee42 My other car is a boat

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    This is a Gen II forum. The gas tanks in your Gen III Prius are entirely different, and as such, your comments should be posted in a Gen III forum.

    Tom
     
    #5 qbee42, Apr 19, 2011
  6. Bob Comer

    Bob Comer Active Member

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    Our gas tanks are definitely different, but the MFD isn't by all that much.

    If anything, i think it's worse for the Gen3, so sorry, I didn't realize I posted in a Gen2 only forum.
     
    #6 Bob Comer, Apr 20, 2011
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