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Tank MPG

Discussion in 'Gen 3 Prius Fuel Economy' started by Indyking, Sep 10, 2009.

  1. TheDJ

    TheDJ New Member

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    That's what I'm seeing. The MID numbers always display the MPG's that are 5% higher than my calculations. I doubt if Toyota will make any adjustments to cars sold. I'm satisfied with either number.

    This is my first Hybrid and I am pleased with the vehicle.
     
  2. a priori

    a priori Canonus Curiosus

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    All you need is to have the last fill point equate to the first fill point. The larger the number of tank fills you have, the less the difference between these two points matters.

    If you've traveled 5,000 miles and had 10 fills, with a total of 85 gallons, then your mileage would be 59MPGs (58.8). If the first fill was a complete top off, but the final fill was short by a couple of clicks, that means you'd have recorded not 85 gallons, but perhaps 84.6 gallons. What is the effect? Mileage would be calculated as 59MPGs (59.1). If you do this calculation again at 10,000 miles, and you've purchased 170 gallons, then your mileage would be 59MPGs (58.8). If you, again, were off by two clicks at the final fill, then you'd have only recorded 169.6 gallons. Mileage would be calculated at 59MPGs (59.0). By 15,000 miles the difference would have narrowed to 58.8 for the final, exact-match top-off and 58.9 for the two-click short final fill. Once you've reached 25,000 miles, there is no way to differentiate: Both would be reported as 59MPGs, again, though you could argue the numbers may be reported as 58.8 and 58.8.

    Of course, I don't know that two clicks would be nearly half of a gallon, but the effect is much the same: The higher the number of miles, the less important the difference between the level of the first fill and the last fill.
     
  3. FreakinToddles

    FreakinToddles New Member

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    My last tank was about 54mpg, I do 95% highway driving @ about 70MPH, so not too bad given the circumstances! Also I used to drive eco mode, but once I realized there was a "normal" mode, I started using that and like it way more than eco mode.
     
  4. Celtic Blue

    Celtic Blue New Member

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    Calculated or indicated? If indicated, then calculated this is likely to about 51 mpg, about the same as my G2 does on the interstate at 70 without excessive crosswind (subtract over 10% for ~20 mph crosswind at 90 degree angle.)

    Indicated is not close to actual mpg in the G3...while my G2's cumulative discrepancy is about 1%.
     
  5. Indyking

    Indyking Happy Hyundai owner...

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    I think it varies. I'm getting about 3% bellow indicated so far. The way I fill up the tank is: set the pump in the lower flow, wait for the first click off, then wait extra 15-20 seconds for those fumes to fade away, and then set it back to the lower flow until the next click off (very quick in the 2010 Prius). That's the way it was recommended by several car engineers in a car magazine I read a good while ago, which source I can't remember.

    I'm not an "evil top off person"!

    I don't care if you have never had problems with topping off your tank. Guess what, I know many people that did have problems in the past and recent with it. So it may not be common event but why the heck take any risk at all! What's the point of getting a 700 miles range for a tank? It's not like I live in continent of Antarctica! (world’s largest desert).The safe 500-mile-range that the Prius is giving me with my fill-up technique is more than sufficient for my needs!!! Also, some people have the wrong impression that they have to top off the tank to get the best estimate of calculated MPG, which is not necessarily true, because, like “a priori” nicely pointed out, as long as you keep your filling-up technique consistent, your calculated MPG will be as accurate as possible.
     
  6. a64pilot

    a64pilot Active Member

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    The only way your going to get accurate results from ONE tank is to find a way to ensure your fill point is the same. I said that in my earlier post, I also said that the accumulative effect would over time average out any errors, the more tanks that you go through the more accurate your results would be, but I wasn't wanting an answer to how inaccurate my FCD was in six months, I wanted an answer in one tank.
    What methodology did you use to determine the accuracy and repeatability of your one click method?
    Who lives in Antartica? and what does that have to do with anything? Truth is, for me this is all for entertainment anyway, I don't need to save the money on fuel, I can afford to burn more fuel, but it's a competition with myself to see what kind of mileage I can eek out of this thing. I enjoy it. I think you would find that since these are all new cars that everyone here could afford to burn more fuel, that almost no one here is making money out of these endevors, and almost all of us are doing it for entertainment.
    What's the point of getting 700 miles to the tank? I guess I can answer that by asking who cares what mileage your getting anyway? Same thing.
    Oh and lighten up, it's all for fun.
     
  7. bluemonday

    bluemonday New Member

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  8. msirach

    msirach Member

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    Double post. Please delete.
     
  9. msirach

    msirach Member

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    As several have said, you must fill up at the same station, same pump, same direction, same clicks, same etc.

    The FCD is off of calculated by 3% to 10%. If your tank averages are over 60 mpg on the fcd, the error will be closer to 10%. I have a case filed with Toyota and the customer rep called me back a couple of weeks ago and said the field engineers are working on the issue and a TSB would be forthcoming. They have acknowledged a large error factor of the FCD versus calculated.
     
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  10. DrJon

    DrJon New Member

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    Just filled up yesterday night for the second official time, so my first full tank where I did the pumping of gas on both sides of the miles. I pump exactly like Indy King to try to keep error as small as possibe. I agree that second click off comes very quickly. Anyway, I used the same exact pump both times. Results:

    WHOOOOOOOOO!!!!!

    701 miles on first tank of my own! MFD said 64.1 at 25 mph but I calculated 60.8 for a 5.15% discrepency. Can I revote on the poll what MPG are you getting in yours?

    So you only need to average about 64 mpg for a tank to get a 700 mpg tank without fear of running out of gas. My tank only took 11.541 gallons on my filling method. I still had almost .4 gal, I think which could have gotten me another 24 miles or so.

    700 mile tank wasn't too dificult, now 800, hmmmmm!

    I live in an area where there is no interstate driving, few stoplights, little traffic and relatively slow posted speed limits.
     
  11. Indyking

    Indyking Happy Hyundai owner...

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    Which is exactly what I said in my post above... i.e. be consistent in all fill-ups... I guess you missed my point in my early post...

    The point is: read the thread title. It says Tank MPG! Rings a bell? It does not say how many miles per tank, does it?

    Here is a suggestion: http://priuschat.com/forums/gen-iii-2010-prius-fuel-economy/68791-700-miles-first-tank-my-own.html

    I opened this thread with the intention to share tank mpg among us. Maybe you still haven't figure that out...

    Lighten up? Are kidding me? I couldn't be more relaxed today... :D:D:D
     
  12. Indyking

    Indyking Happy Hyundai owner...

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    Here is the link for Bob's data:

    http://priuschat.com/forums/gen-iii...1-700-miles-first-tank-my-own.html#post955735

    Very nice.

    You can see that getting indicated MPG of 70+ (actually 75+) at 20 MPH is pretty much average... :)
     
  13. FireEngineer

    FireEngineer Active Member

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    I hate being average, but I love the start to a good tank.

    P1000827.JPG

    Wayne
     
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  14. angelrob

    angelrob New Member

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    LOL yeah, pulling out of the gas station at 99.9 for the first block...and then, it passes. My current tank is hanging around 60 at 200 miles. At 88 miles, I topped off my tires to 40/38. It was still at 60 at that point, but I've held it now for two round trips to work. Could be my increasing mileage and skill, could be the tires. I'm going to keep them at this pressure for a few tanks and see.

    I'm also going to keep up my current filling procedure for a while before I try to add more per the alternative fill instructions...just to keep things "the same" (ish :p)

    Robbin
     
  15. DrJon

    DrJon New Member

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    So, if you are already exceeding Toyota placard for recommended tire pressure, why not go up to at least the tire manufacturer's max of 44 psi? Careful though, you might pop them (at 130 psi!!!) LOL!
     
  16. DaveinOlyWA

    DaveinOlyWA 3rd Time was Solariffic!!

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    yes that is a surprise. there are many threads tracking tanks to illustrate the inaccuracy of the MFD mileage numbers

    my last tank and average speed is listed in my signature. not by best, just my last one. my average speed is low because 3-4 times a week, i pick up my son at grandma's house. i leave the car "running" so it will sit anywhere from say 5 minutes to as much as 15-20 minutes. obviously not the thing to do for the longer waits... but it happens. so i guess i dont "qualify" for your tank considerations?

    ok. now if purposefully driving around to get good mileage is what you are doing, then why bother??. are you upset that someone is getting better mileage or that they have a better commute than you do? your assumption that someone is driving to get better mileage at the risk of being late to work or losing your job is ridiculous

    now, that latter statement is much closer
     
  17. DaveinOlyWA

    DaveinOlyWA 3rd Time was Solariffic!!

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    ah ya Wayne...with 2 battery bars left, all i can say is why is it not 99.9??

    as far as mileage and fillups goes. i fill as top speed (i have better things to do than to spend 1893% more time filling the Pri than i do the Zenn!!) first click. immediate calculation based on miles driven as to whether i am close to full. (not a math wizard!!) if close. stop, if not go another click. i always have a rounded gallon figure in my head when i stop to fill up anyway.

    granted, because the MFD is so far off, i always shoot pass my target number. i am ok with that since my LT stats are the only thing that really matters.
     
  18. bwilson4web

    bwilson4web BMW i3 and Model 3

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    More data points:
    [​IMG]

    [​IMG]

    [​IMG]

    Bob Wilson
     
  19. Indyking

    Indyking Happy Hyundai owner...

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    Again...again...and again....

    Not very useful MPG data in my opinion!

    come on.. 14.2 miles only? ???? 15 mph????

    my mom can do that... :D:D:D
     
  20. Indyking

    Indyking Happy Hyundai owner...

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    Let me clue you in mate:

    http://priuschat.com/forums/gen-iii-2010-prius-fuel-economy/68738-tank-mpg-5.html#post954986

    I hate when people post unpleasant posts because they are not following the whole thread, therefore, don't really know the whole story... chill out.... life is good :cool:

    I'm not competing with anyone, never intended to do so!

    I'm really interested to know how far we can push our Priuses for fuel efficiency. It's all for the benefit of everyone, hopefully. So far, I believe I haven't seen anybody getting a tank MPG (at least 500 miles) of 63+ at average speeds over 31-32 MPH...it will be cool and interesting to see if anyone can do better than this...

    Feel a little better now, maybe?