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How do you keep track of fuel mileage on a Prius?

Discussion in 'Gen II Prius Fuel Economy' started by PriusPhilly, Mar 10, 2012.

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  1. PriusPhilly

    PriusPhilly Junior Member

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    OK I have an excellent question;

    How do you guys keep track of the Prius fuel mileage knowing the bladder in the tank changes size depending on the temperature??

    Wouldn't that make it impossible to keep track of mileage? I live in Montreal Canada and the temperature varies from -35ºC(-31ºF) to +35ºC(95ºF) so the temperature is constantly changing throughout the year.

    Usually when you calculate your mileage, you take the distance traveled since your last fill up and the amount of fuel it takes to fill up the gas tank.

    But with the Prius gas tank, that accepts different amounts of fuel depending on the temperature, it throws that calculation all off.

    Since I see everyone on this site calculates their mileage and posts it up, how do you guys go about doing it. Is there a special technique?

    Thanks!
  2. Mendel Leisk

    Mendel Leisk Senior Member

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    Calculation for one tank could be off, but the next tank, or the one after that, should balance it out. And if you calculate accumulating mileage and distance, it will be very accurate, regardless of any variation in tank capacity. For example: a calculation for all the gas you pumped in a year, and the total distance travelled.
  3. jadziasman

    jadziasman 75K miles to go before the odometer stops

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    Exactly correct. That's how I calculate fuel economy. Over a long time scale.

    I do wonder some times how accurate the fuel delivery pumps are. Sometimes I sense I'm being cheated by some gas stations. I haven't gone to the extreme of filling certified 5 gallon gas containers and complaining to the gas station if I don't get the full 5 gallons. If regular reaches $5/gal average across the continental US, I think you might see people who will do this.
  4. Mendel Leisk

    Mendel Leisk Senior Member

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    The one downside though: if you want to see short term mileage, it's going to be difficult with a finicky gas tank. At least you can use the dash display for that, keeping in mind that it might be exxagerating by some percentage.

    On that subject, early reports from Plug-In Prius owners are saying that the displayed mileage is finally quite accurate.
  5. Kmack

    Kmack New Member

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    For all the Canadians out there... Here's an easy basic sheet that I put together and have been using (including my gas mileage for the first few months) - Size of tank is not in the calculation, rather, you put in the mileage (kilometers) you travelled and number of litres to fill back up. you need to reset one of your your trip odometers or use the reading from the MFD that resets automatically every fill-up (not sure if it's linked to Trip-A, but mine seems to reset by itself on fill up once the car moves a bit). I keep my receipts in the glove box and add up the used litres between actual fill ups so i don't have to fill every time if the price is too high. I only reset/calculate when I put in an actual full tank.

    And before you ask, yes, my mileage is that bad in winter, typically -10 or lower for the winter months and the ICE runs alot for heat.


    Feel free to modify, and pass it on.

    Attached Files:

  6. navguy12

    navguy12 Member

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    Same here. Over the long term......
  7. qbee42

    qbee42 My other car is a boat

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    You don't get to grade your own questions. ;)

    I'd give this one a 'B' grade at best: It's a decent question, but it's been asked and answered many times before.

    Tom
  8. Michgal007

    Michgal007 Senior Member

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    I have recorded on-screen mpg and miles for each tank (plus price of fuel) for 5+ years now. One of these days I should make some pretty graphs.
  9. Big Steve

    Big Steve ramblin wreck

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    Here is a modified version which gives a three-fillup moving average and should average out the variation over a few fillups. I don't like the lifetime average because it masks other changes.

    (Finally a question here about something I know, spreadsheets!):eek:
  10. Big Steve

    Big Steve ramblin wreck

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    And maybe now ith the attachment

    Attached Files:

  11. navguy12

    navguy12 Member

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    OK, here is my spread-sheet version. Enjoy.

    Not many data points yet, but I figure no one here would want to look at 5 years of data from my '07 HCH.....

    Once you open it, select the view summary page.....

    Attached Files:

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