Extremely Bad Gas Mileage

Discussion in 'Gen 2 Prius Fuel Economy' started by MaddieS, Nov 7, 2018.

  1. MaddieS

    MaddieS New Member

    Joined:
    Nov 7, 2018
    1
    0
    0
    Location:
    Charlotte, NC
    Vehicle:
    2007 Prius
    Model:
    N/A
    Hi all! I’ve solved a lot of my Prius problems through this chat so I decided to reach out. I have a 2007 Prius that was bought new. It reached 200,000 miles a few weeks ago and I started getting only around 250 miles per tank, a full tank would take about 8 or 9 gallons. I’m now at 205,000 miles and I’m only getting 160 miles per tank. It’s still telling me that I’m receiving 45 miles per gallon but I don’t believe that’s true. My tire pressure is fine and I’ve kept up to date on all of the needed replacements etc. Has this happened to anyone?
     
  2. Tideland Prius

    Tideland Prius Moderator of the North
    Staff Member

    Joined:
    Oct 2, 2004
    39,817
    11,343
    40
    Location:
    Canada
    Vehicle:
    2018 Prius Prime
    Model:
    Technology
    The rubber bladder inside the fuel tank is notorious for varying the tank size (and shrink as it ages); although 160 miles is really low and can't all be explained by the bladder.

    Did you recently have an oil change? Check to see that the oil level is correct and not overfilled.

    Check the engine air filter, maybe it's dirty, resulting in low airflow and poor fuel-air mixture.
     
    Raytheeagle likes this.
  3. TMR-JWAP

    TMR-JWAP Senior Member

    Joined:
    Aug 12, 2016
    2,251
    2,743
    0
    Location:
    Columbia, SC
    Vehicle:
    2007 Prius
    Model:
    Touring
    The mpg displayed by the car is calculated using fuel curves/pressure/injector duration/all those fancy things floating around in the ECU/etc. Considering the car's electronics are still showing normal mpg, yet actual miles per tank are extremely low (yet fill volume is normal........I would focus some attention on looking for a fuel leak.

    Know what I mean? The engine IS getting 45 mpg, it's just that only half of the gas in the tank is going to the engine. The rest is going onto the ground or into the air.......maybe....
     
    jerrymildred likes this.
  4. bisco

    bisco cookie crumbler

    Joined:
    May 11, 2005
    82,347
    35,806
    0
    Location:
    boston
    Vehicle:
    2012 Prius Plug-in
    Model:
    Plug-in Base
    fill the tank, reset the trip meter, drive until the last pip, refill and divide miles by gallons pumped and report back
     
    James1964 and PA Prius like this.
  5. jerrymildred

    jerrymildred Senior Member

    Joined:
    Oct 28, 2016
    6,077
    7,666
    0
    Location:
    Tampa, FL
    Vehicle:
    2017 Prius Prime
    Model:
    Prime Premium
    There ya go, gettin' all logical. Again. :D

    I have to agree with this. If the car says it's getting 45 mpg, then that's what the engine is getting. Well, almost 45 anyway. If you're putting 8-9 gallons in the tank to go 160 miles, then obviously, most of the gas isn't reaching the engine. I would think that that would cause a big stink. Literally.
     
    padroo likes this.
  6. TMR-JWAP

    TMR-JWAP Senior Member

    Joined:
    Aug 12, 2016
    2,251
    2,743
    0
    Location:
    Columbia, SC
    Vehicle:
    2007 Prius
    Model:
    Touring
    Maddie????

    Hope you were able to resolve the problem. Yes or no, please let us know. The more feedback that gets posted, the better our "well of knowledge" becomes.
     
  7. douglasjre

    douglasjre Active Member

    Joined:
    Sep 13, 2008
    373
    156
    0
    Location:
    Orlando, FL
    Vehicle:
    2010 Prius
    Model:
    ----USA----
    Those don't effect fuel economy.
     
  8. Tideland Prius

    Tideland Prius Moderator of the North
    Staff Member

    Joined:
    Oct 2, 2004
    39,817
    11,343
    40
    Location:
    Canada
    Vehicle:
    2018 Prius Prime
    Model:
    Technology
    A dirty air filter would (Edit: No it doesn't) . But the shrinking bladder won't (but could be one of the contributors to the lower range)
     
    #8 Tideland Prius, Nov 13, 2018
    Last edited: Nov 14, 2018
  9. padroo

    padroo Senior Member

    Joined:
    Jan 11, 2008
    2,754
    2,203
    13
    Location:
    Chesterton, Indiana Another third world country.
    Vehicle:
    2016 Prius
    Model:
    Four
    Those Gen 2 gas tank bladders got you by reducing the amount of fuel you can put in the tank and on top of that cold weather makes it seem much worse than it is.
     
  10. douglasjre

    douglasjre Active Member

    Joined:
    Sep 13, 2008
    373
    156
    0
    Location:
    Orlando, FL
    Vehicle:
    2010 Prius
    Model:
    ----USA----
    I'm sorry tideland, a dirty air filter does not effect fuel economy. To be politically correct is to not correct you so I'm not going to be politically correct but I'm also not going to put it in a lot of time trying to teach you this one. You're going to have to teach this one to yourself I'm sorry. the same token that cannot let you propagate false information as though it were correct just because it is your belief system.

    I'm an ase-certified mechanic and a practice medicine now because I went to school for a long time so I didn't have to be a mechanic anymore. You need to learn what a mass airflow sensor is. You need to learn how the system adjusts to the amount of air that goes through so that the fuel ratio remains constant no matter how dirty and air filter is. an oxygen sensor monitors to confirm that the fuel ratio is stoichiometric. The mass airflow sensor recognizes the correct amount of air flow even if the throttle vane is wide open but the air filter is kind of dirty.
     
    #10 douglasjre, Nov 14, 2018
    Last edited: Nov 14, 2018
    Tideland Prius likes this.
  11. douglasjre

    douglasjre Active Member

    Joined:
    Sep 13, 2008
    373
    156
    0
    Location:
    Orlando, FL
    Vehicle:
    2010 Prius
    Model:
    ----USA----
    Unsubscribed from this topic because I don't feel I'm learning anything here.
     
  12. Tideland Prius

    Tideland Prius Moderator of the North
    Staff Member

    Joined:
    Oct 2, 2004
    39,817
    11,343
    40
    Location:
    Canada
    Vehicle:
    2018 Prius Prime
    Model:
    Technology
    Roger that. Sorry :( I will go pick up a book (well I guess a digital book).
     
  13. jerrymildred

    jerrymildred Senior Member

    Joined:
    Oct 28, 2016
    6,077
    7,666
    0
    Location:
    Tampa, FL
    Vehicle:
    2017 Prius Prime
    Model:
    Prime Premium
    Poor @MaddieS! I think you guys ran her off. I wonder if she's still only getting 160 miles on 8 or 9 gallons of gas. Remember the original question?

    I hope she comes back, because with enough info, there's a good chance someone like @TMR-JWAP can point her in the right direction.
     
    Mendel Leisk likes this.
  14. douglasjre

    douglasjre Active Member

    Joined:
    Sep 13, 2008
    373
    156
    0
    Location:
    Orlando, FL
    Vehicle:
    2010 Prius
    Model:
    ----USA----
    You're right about that. I've found diagnostic suggestions don't often get result in success when done by text messages. The person with hands on the problem needs to be armed with knowledge plus tools plus wisdom and much of that comes from experience. As listeners we attempt to guide the diagnostics but it doesn't always help unfortunately.

    most of all after somebody has solved the problem they don't follow up and give us the answer to what they discovered. There's often no closure. This is where we all can benefit from this discourse but many times do not. Hopefully she does respond so that we can add this causative agent as a differential for the next person who has a similar problem.
     
    jerrymildred likes this.
  15. 05PreeUs

    05PreeUs Senior Member

    Joined:
    Oct 1, 2016
    1,001
    488
    0
    Location:
    MSP
    Vehicle:
    2005 Prius
    Model:
    N/A
    You are comparing "miles per TANK" and "miles per GALLON", those measures do not measure the same thing. If you used cost per mile, that would likely be the same no matter how much or little fuel you put it during refueling.

    MPG = Miles driven / gallons used (# off the pump)

    MPT = Miles driven before you fill (could be 1 or 500) which has nothing to do with MPG.
     
  16. audiodave

    audiodave Active Member

    Joined:
    Feb 3, 2017
    621
    224
    0
    Location:
    US
    Vehicle:
    2004 Prius
    Model:
    Five
    If the engine can't breathe the way it was designed I'm sure it would affect fuel economy.

    Posted via the PriusChat mobile app.
     
    bisco likes this.
  17. 05PreeUs

    05PreeUs Senior Member

    Joined:
    Oct 1, 2016
    1,001
    488
    0
    Location:
    MSP
    Vehicle:
    2005 Prius
    Model:
    N/A
    Actually, it does, but the effect is so small most could not measure it. The ECM injects the EXACTLY correct amount of fuel for the air that does get in and not a drop more. Power can be significantly affected by a plugged air filter, that is proven and why race cars do not have them.
     
  18. audiodave

    audiodave Active Member

    Joined:
    Feb 3, 2017
    621
    224
    0
    Location:
    US
    Vehicle:
    2004 Prius
    Model:
    Five
    Yes but if you noticed a power difference you would notice a milage difference. But it would need to be plugged. Lol

    Posted via the PriusChat mobile app.
     
  19. bisco

    bisco cookie crumbler

    Joined:
    May 11, 2005
    82,347
    35,806
    0
    Location:
    boston
    Vehicle:
    2012 Prius Plug-in
    Model:
    Plug-in Base
    now that doug is no longer here, i'm sticking with 'clogged air filter affects fuel economy'

    and if i get sick in florida, i hope that's his real first name

    not tobe pedantic or anything
     
    James1964 likes this.
  20. Mendel Leisk

    Mendel Leisk Obtuse Angler

    Joined:
    Oct 17, 2010
    35,209
    24,076
    80
    Location:
    Greater Vancouver, British Columbia, Canada
    Vehicle:
    2010 Prius
    Model:
    Touring
    The only apparent problem is the low miles-per-tank, which (as @Tideland Prius first noted) is likely due to the 2nd gen tank having a "flexible" bladder, which can contract/restrict.

    The dash display is saying 45 mpg, which is good. I wouldn't quite believe it, but only because Toyota likes to BS the displayed mpg, about as much as they can get away without it becoming blatantly embarrassing. Actually, I think they've crossed that line, have no pride, lol.

    Instead of just believing or not: calculate it, see for yourself. At every fill up, record the gallons of gas put in, and the miles since last fill up. Divide the gallons into the miles; that's your miles-per-gallon (mpg)

    My understanding from what I've read: that used to hold true in the manually tuned carburetor days, but with computer controlled fuel-injection, with sensors detecting the air flow, the amount of O2 in the exhaust, knocking, fine-tuning the injector sprays accordingly, you can be running low octane and a dirty air filter, still do fine.

    In fact a partially clogged air filter might improve mpg, you're sorta reducing the engine displacement, the volume of air. I've heard the only time air filter clogging matter is if it's virtually blocked.
     
    #20 Mendel Leisk, Nov 22, 2018
    Last edited: Nov 22, 2018
Loading...