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How accurate is the consumption on the Prius for mpg?

Discussion in 'Gen 2 Prius Fuel Economy' started by Banksy, May 2, 2020.

  1. Banksy

    Banksy Active Member

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    So I'm curious.

    My consumption is saying over 223 miles I'm getting 48.9 mpg

    However I am at a half take currently for this trip meter and am at 223 miles.

    It's a 12 gallon tank right? So that's mean this car has used six gallons of gas and is getting 37ish mpg.

    How is the consumption of the car saying it's getting nearly 49 mpg?
     

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  2. ydpplqbd

    ydpplqbd Active Member

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    MY 2006 Gen2 Prius is getting about 50mpg +/- 1 mpg now that it is warm (extended warm-up periods found in winter are now a thing of the past). However, my MFD displays about 47mpg to 48mpg usually. IOW, the MFD underestimates my gas mileage by six to seven percent ("6% to 7%"). Thus, minimum gas mileage currently (based on above facts and after correcting MFD) is 49.82mpg (1.06 x 47 mpg). While, maximum gas mileage currently (based on above facts and after correcting MFD) is 51.36mpg (1.07 x 48 mpg). My understanding is that most Gen2 MFDs overestimate mpg (however, my MFD does the opposite: underestimates).

    Last fill-up was 9.1 gallons. Thus, I expect to travel about 460.4 miles on this tankful of gas ((49.82+51.36)/2 x 9.1). My gas gauge is most accurate and helpful when I was at the half tank point (5 pips, AKA as blins, left on the gas gauge). With 5 pips left on the gas gauge, the odometer showed that I had traveled 230 mile since last fill-up (and implicitly that the full tank should last for 460 miles before the next fillup: 230 miles x 2=460). Essentially, I treat the gas gauge as broken except when i.) gauge shows 10 pips and thus, it is treated as completely full; or ii.) has five ("5") pips remaining (AKA half full).

    Banksy, if your Gen2's MFD works like mine (namely, underestimates gas mileage) then the projected range for your car is 446 miles on this tank of fuel (223miles x 2= 446 miles).

    PS When I first got this car, it was only taking 6.5 gallons to fill it. By driving the car to the full extent of its projected range (as described above) before refueling, the car has slowly but surely taken more fuel at each fill-up (this process has been ongoing for the last four months)..

    PPS Typically, 5 pips remain lighted for about 12 to 15 miles and then the 5 pip is extinguished. And, I only have four ("4") pips illuminated.
     
    #2 ydpplqbd, May 2, 2020
    Last edited: May 2, 2020
  3. bisco

    bisco cookie crumbler

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    mine is spot on, but i don't have a blatter
     
  4. Banksy

    Banksy Active Member

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    So what your saying is yes they are accurate

    And that I should basically wait until the fuel light comes on to do my mpg to cross check with the readout?
     
  5. George W

    George W Active Member

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    I put pen-to-paper with odometer and fuel receipt. It usually matches the car's estimated economy within plus or minus 1.5.

    Are you resetting your consumption in between fill-ups?
     
  6. Banksy

    Banksy Active Member

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    What difference does it make?

    I should probably just wait until it reads empty
    But I know I put 12 gallons in this tank

    So I'm just wondering why the maths aren't adding up
     
  7. Banksy

    Banksy Active Member

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    Well this most recent consumption was right after I pulled the 12v battery

    And the readout says for the same amount of Miles as the trip so I'm figuring it's reset and current information
     
  8. George W

    George W Active Member

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    The longer you go without resetting your consumption, the more the computer averages your mileage over increasing distance driven
     
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  9. sam spade 2

    sam spade 2 Senior Member

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    Everything you quoted is guess work.
    The onboard calculation of fuel mileage is almost always a little high it seems.
    If it says 49, then 45 would be more realistic.
    But you can't "estimate" the fuel usage to get a better figure.
    You know the miles; now you need to note the gallons on the next couple of fills and do the math.
     
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  10. Banksy

    Banksy Active Member

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    Thank you sam!
     
  11. The Electric Me

    The Electric Me Go Speed Go!

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    I know it's not helpful, but I've spent most my life wondering why the maths aren't adding up.
     
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  12. Mendel Leisk

    Mendel Leisk Senior Member

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    The Brits have and expression, think I'm gonna "keep shtum". I was gonna go into a step-by-step, on how to calculate mpg, but suspect it'd be confetti in the wind.
     
  13. Banksy

    Banksy Active Member

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    I do not know

    I just take the amount of miles I've done and decide it by the gallons of gas I put in the tank
     
  14. Mendel Leisk

    Mendel Leisk Senior Member

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    Apologies, you nailed it. (y)
     
  15. George W

    George W Active Member

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    To get consistent results, you must refuel the same way consistently. The gen 2 Prius' fuel bladder changes with age, air pressure, temperature, and even differences in the way you 'fuel'.

    There are plenty of threads here about the Gen 2 bladder. The best result is to refuel the same way every time (stop at the click-off, don't top off). That way you have a repeated pattern to base a useage from.
     
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  16. Mendel Leisk

    Mendel Leisk Senior Member

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    Another tip: you "can" determine your miles travelled with a trip meter, but they can be accidentally reset. More bullet proof is to record the odometer at each fill up, subtract the previous reading from current.

    I do both, trip meter and odometer, check one against the other, but the odometer is the ace-in-the-hole. :)
     
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  17. Banksy

    Banksy Active Member

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    Oooo that's a good point

    I totally topped this off

    Ohhh well let's drain that bladdah and get some accurate figures
     
  18. Banksy

    Banksy Active Member

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    Good point I'll give it a shot
     
  19. Banksy

    Banksy Active Member

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    Also can somebody explain the arrows to me that are on the energy screen?

    I've noticed when they are all active the car gets the worse mpg.

    And when the Orange one in the front is active it gets the best mpg?

    I'm assuming the icons are for the engine, the electric assist and the battery?


    It's kind of got me confused and I think maybe my over all mpg when this is over maybe be due to driving technique.

    I generally have had this screen off due to for me it's a distraction because I know I'll obsess over it and have just checked the overall consumption from time to time

    I've just been basically applying the least amount of pressure to the accelerator as possible and using it not at all if possible.

    Perhaps this isn't the proper approach with a prius. My thought has been..less use of the gas better mpg.

    Some clarification and tips would be greatly appreciated

    Excuse my ignorance if this sounds dumb or like I don't know what I'm talking about because to be absolutely frank that is absolutely the case

    I have no frigging idea and am just trying to use logic to figure this out :whistle::whistle::whistle::rolleyes::rolleyes::rolleyes:

    Thanks in advance for your time I really appreciate it.
     
  20. Philjj

    Philjj Junior Member

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    The arrows show where the energy is coming from and going to, and change color to let you know the electrical advantage/disadvantage from the operation you are doing in terms of fuel consumption. A definite distraction especially at the start of ownership. The screen has a number displayed at the bottom, which is actual consumption at that instant, if I am stopped and the motor is running it shows 99.9 litres per 100km. The best way to understand, as per usual is to RTFM which stands for Read The F***ing Manual. Downloading is easy, Cheers.