1. Attachments are working again! Check out this thread for more details and to report any other bugs.

Fuel Refill vs Display...

Discussion in 'Gen 2 Prius Fuel Economy' started by cdub1955, Apr 18, 2008.

  1. cdub1955

    cdub1955 New Member

    Joined:
    Apr 12, 2008
    18
    0
    0
    Location:
    Lexington, KY
    Vehicle:
    2007 Prius
    I am having some trouble with MPG, based on what the display shows vs what I might get if I calc based on refill.

    1. Let me tell you this is my first refill, and I was a bit surprised to find that I had to go to two stations to get the tank filled up. The first time it stopped, and could not take any more fuel (I did use the lowest setting...), but it obviously is too fast. It filled the tank to half full. I then pulled out and went a couple blocks to another station and was able to 'slowly' put another 4 gallons into the tank. It shows full.

    2. My display showed 50.2 mpg, but if I calc it based on refill it was actually only 37 mpg. Of course I have no idea how it was 'filled' in teh first place and given the 'bladder' who knows really.

    Is the display reliable?

    Any 'advice' on refil, or 'training' the bladder to be more accepting of a refill?

    Thanks,
    Chris
     
  2. NYPrius1

    NYPrius1 Active Member

    Joined:
    Jul 7, 2007
    1,181
    125
    0
    Location:
    Middletown, NY
    Vehicle:
    2007 Prius
    Hi Chris,
    I usually fill up and than go one more click. Than stop.
    The MFD and my hand method differ less than 1 MPG.
    Hope This helps.
     
  3. Austin50mpg

    Austin50mpg Prius Driving Right Winger

    Joined:
    Apr 10, 2008
    197
    1
    0
    Location:
    Austin
    Vehicle:
    2008 Prius
    The individual stores can set the rate at which gas flows from the pump. I would try to find a gas station that pumped slow to medium. There are two gas stations close to my home. One will pump the gas so fast it shoots gas out at me sometimes after the click. The other station pumps gas so slow I become impatient. I have not used the "hyper pump" station since I purchased my Prius.

    50.2 vs 37 seems to be way off. In my experience is the MFD will be within +/- 1MPG using my calculations according to the pump measures.

    How many total gallons were you able to place in your first fill up?
     
  4. charansr

    charansr Member

    Joined:
    Mar 25, 2008
    107
    0
    0
    Location:
    Concord CA
    Vehicle:
    2010 Prius
    Model:
    IV
    Results after 1st fill :

    MFD : 42.6
    Calc : 40.3
     
  5. efusco

    efusco Moderator Emeritus
    Staff Member

    Joined:
    Nov 26, 2003
    19,891
    1,193
    9
    Location:
    Nixa, MO
    Vehicle:
    2004 Prius
    Model:
    N/A
    Also, there's no telling how "full" the tank actually was when you took delivery. Also, it's likely that you over-filled a bit by using the two different pumps.
    Trust the MFD for tank to tank mpg, trust the calculated method for lifetime numbers.
     
  6. cdub1955

    cdub1955 New Member

    Joined:
    Apr 12, 2008
    18
    0
    0
    Location:
    Lexington, KY
    Vehicle:
    2007 Prius
    I had 1 pip showing on the gage, and it showed I had driven 302 miles on the tank. The gauge was 'full' when I purchased, but again I did not fill it up, so who knows really.

    I was able to put 8.2 gals into the tank, which really comes out to about 37 mpg, while the MFP showed 50.2.

    I will try some of these 'methods' here...and see how I do. Is it possible to 'teach' the bladder to be more accepting of a full tank. as an example, what if I fill more frequently for a while, leaving say 3/4 to 1/2 of a tank full at all times? Any experience with that?

    FYI, I was pleased with my mpg as far as the MFP was giving me...

    Chris
     
  7. Austin50mpg

    Austin50mpg Prius Driving Right Winger

    Joined:
    Apr 10, 2008
    197
    1
    0
    Location:
    Austin
    Vehicle:
    2008 Prius
    I haven't tried the train the bladder game. Looking around PC it doesn't seem to make a difference. According to most PC members it is based more on outside temps.

    Toyota should have this issue better documented. I was hoping to use at least 11 of the 11.9 listed gallons and go nearly 600 miles before fills. No dice. The most I have put in my tank is 9 gallons. Of course I have not let the last PIP blink yet either.
     
  8. morpheusx

    morpheusx Professor Chaos

    Joined:
    Mar 6, 2007
    1,555
    81
    0
    Location:
    Akron, OH
    Vehicle:
    2011 Prius
    Model:
    Three
    You can still squeeze 600 miles out of a tank. I've managed a few. This summer I hope I can squeeze out at least one 700 mile / 70 MPG tank.
     
  9. cdub1955

    cdub1955 New Member

    Joined:
    Apr 12, 2008
    18
    0
    0
    Location:
    Lexington, KY
    Vehicle:
    2007 Prius
    I was afraid to let the last pip blink, but maybe I need to do this once, just to know what is happening with my guess gauge?
     
  10. mglindsey

    mglindsey New Member

    Joined:
    Apr 17, 2008
    8
    0
    0
    Location:
    Milwaukee, WI
    Vehicle:
    2007 Prius
    I'm very new here, so excuse me for just jumping in. I have owned my 07 Prius since last September. Then took it to Florida with me this Christmas. I have gone from warm to cold to warm weather and will tell you that temp has a LOT to do with it (mileage as well as gas tank capacity). In colder weather the tank will not come close to holding a full tank. To offset I can keep clicking away past "full," and still have the gas gauge show less than full.

    It seems to me that calculating mileage is a very tricky issue with a Prius. This is true for 2 reasons: 1.) No one really knows exactly how much gas is left in the tank when you fill. So, fill-to-fill calculations are sketchy at best. I have always trusted my display and traveling the same distance and route to work and back have seen my #'s fluctuate wildly based on (92 miles each way on an interstate highway): road grade, temperature, wind speed and direction (a big one). I have gotten as low as 36.9 and as high as 52.6.

    I have NEVER gotten close to 600 miles on a tank.
     
  11. Austin50mpg

    Austin50mpg Prius Driving Right Winger

    Joined:
    Apr 10, 2008
    197
    1
    0
    Location:
    Austin
    Vehicle:
    2008 Prius
    By squeeze due you mean a blinking PIP? If not I cant wait to see what MPG I get in August when it sometimes 107 F in the shade.
     
  12. arf1410

    arf1410 Junior Member

    Joined:
    Jan 31, 2008
    47
    0
    0
    2000 miles into a 2008 prius, and I have done mpg checks at fill-up 4 times...and calculating 43-44 mpg...which is consistent with EPA results. MFD generally states 47-48 mpg range, almost 10% higher...I must believe calculating it the old fashioned way is more accurate.

    As a side note, my 2004 Sienna has an LCD mpg display, which typically runs ~10% higher than manually calculating it, and they may very well have the same MPG calculating system...
     
  13. morpheusx

    morpheusx Professor Chaos

    Joined:
    Mar 6, 2007
    1,555
    81
    0
    Location:
    Akron, OH
    Vehicle:
    2011 Prius
    Model:
    Three
    Calculating manually is only accurate when calculating several tanks, there is no way to be sure you added the exact same amount of gas that was used.
    For example say you calculated 4 tanks at once. With the 4 fill ups you added a total of lets just say 35 gallons and travelled 1800 miles. you would have about 51 MPG hand calculation. But if it is warmer outside then your last fill and you only calculated a single tank (most likely added an extra gallon) say you only got 425 miles and then added 9 gallons this time, a computer display of say 53MPG now becomes a 47MPG hand calculation because of the extra gallon you were able to fill this time.
     
  14. arf1410

    arf1410 Junior Member

    Joined:
    Jan 31, 2008
    47
    0
    0
    Huh??? Your going to have to show me some hard data to convince me the density of gasoline vaires by more than about 1% in normal temp swings...

    edit - just verified it would take an 18 F change to cause a 1% change is gasoline density. And keep in mind, this is not in ambient temperature, but in the temp of a large mass of an underground liquid reservoir. So except in the most unusual temperatures variation over fill-ups that were widely spaces, temperature will not affect the gasoline density in a measurable way...

    So can someone try again to tell me what I dont understand?
     
  15. morpheusx

    morpheusx Professor Chaos

    Joined:
    Mar 6, 2007
    1,555
    81
    0
    Location:
    Akron, OH
    Vehicle:
    2011 Prius
    Model:
    Three
    Here is the easiest way to explain it. The Prius has a bladder inside the fuel tank, it is able to stretch more when its hot and less when its cold. Meaning that the size of the gas tank varies from fill to fill. Do a search here for "bladder" and then you will understand.