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Consumption Screen Accuracy?

Discussion in 'Gen II Prius Fuel Economy' started by ChiPri, Jan 24, 2006.

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  1. ChiPri

    ChiPri New Member

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    Hi. This is my first post on PriusChat. I'm the proud new owner of an '06 barcelona red, pkg 8. I love the car and the color!

    Here's my question... How reliable is the information on the consumption screen supposed to be? I ask this because I have noticed several 5 minute intervals where the car will mostly be in electric, with 10 - 20 seconds here or there of the ICE kicking in (say during really bad traffic on the highway), and the 5 minute snapshot reading comes in pegged at 100 mpg! What's with this? The car clearly can not be getting 100 mpg if the ICE kicked in. I'm now wondering if most 5 minute readings are overstating the truth.

    Anyone else notice this apparent glitch?

    Thanks!
  2. tomdeimos

    tomdeimos New Member

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    If the engine runs a few seconds out of 5 minutes your mpg had better be way over 100 mpg, unless you weren't moving during the other 3 or 4 minutes.

    The gauge is accurate. Most owners that have tested it over a dozen or more tanks find it within 2 %. Mine came out witin about 1% accuracy.
  3. bobr1

    bobr1 New Member

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    Well, if you think about it, at the times when you are running entirely on electricity or are regenerating, you are consuming no gasoline at all at that instant. This means you are actually achieving infinite miles-per-gallon. Eventually, the battery will need to be recharged, and the ICE will come on, and lower your MPG in future consumption readings.

    Toyota had insufficient room on the dash for a MPG bar that went to infinity, so they cap it at 100MPG. :)

    Another way of looking at it... suppose you are coasting down a very, very long hill for 99 miles, not consuming a single drop of gas, batteries being charged by regen. Then, at the bottom, there is a short but steep 1-mile incline. Say that you consume a full gallon of gas climbing this incline. You'll still have gone 100 miles on 1 gallon of gas, or 100MPG!

    So it is quite possible that the Consumption screen is not lying to you just because the ICE runs a bit now and then.

    - Bob R.
  4. ChiPri

    ChiPri New Member

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    Thanks for the responses! I was overlooking the fact that the 100 mpg mark really just represents infinity in full electric mode. Glad to know I can have full faith in the results.
  5. San_Carlos_Jeff

    San_Carlos_Jeff Active Member

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    Just today I entered in to a spreadsheet all my gas usage data for the first 5000 miles of my car (2005). Was pleasantly surprised at how accurate the computer is.

    The actual average mileage was 45.2mpg
    The average mileage the computer calculated was 46.0
  6. pgorbas

    pgorbas New Member

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    I figured the 'gage' maxed out at 99.9 mpg - but this is actually pretty poor design - the display is a LCD screen, not a little digital display which can only show numbers ---when the car is running 100% electricity it would have been easy enough to put a infinty sign(∞) in for the instant mpg.
  7. kpauley

    kpauley New Member

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    I have 13 tanks into my 2005 now and I have been tracking the MPG on the MFD compared to what the display says on each tank.

    The worst I have seen is a 10% difference (a little over a 4 MPG difference) between what the MFD is stating and what the actual mileage is. Haven't really come up with a pattern yet as to why it seems to vary for me.

    The attached spreadsheet has the numbers if you are curious

    Ken
  8. San_Carlos_Jeff

    San_Carlos_Jeff Active Member

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    Tank to tank I get wildly differnent numbers vs. the display. That's because it's so hard to get a consistent fill on this gas tank. I was surprised that when checking the cumulative numbers it was so close.
  9. aforkosh

    aforkosh Member

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    At the beginning of this year, I ran a comparison between mpg via my mileage log and the consumption screen for my 2004 Prius. I posted the spreadsheet on this forum at this link. Note that I realized a minor problem with the 1st attempt and posted a corrected spreadsheet on a second message.

    The general conclusion was that over approximately 15,000 miles, the screen readings came up 3 miles short and the calcuated usage from the screen was 8.4 gallons short. Thus, the screen mileage was 2.73% higher (47.9mpg vs. 46.6mpg) than the mileage log computation.
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