Found the answer to low MPG

Discussion in 'Gen 3 Prius Fuel Economy' started by epcotfilmguy, Oct 15, 2019.

  1. epcotfilmguy

    epcotfilmguy Junior Member

    Joined:
    Dec 17, 2011
    1
    5
    0
    Location:
    Hickory, NC
    Vehicle:
    2010 Prius
    Model:
    Four Touring
    Over the past several years I had noticed a gradual decrease in fuel efficiency in my 2010 Prius with 122K miles. I tried everything to get it to come up from the 43-45mpg range. I did everything people recommended, a wheel alignment, fuel injection cleaning, changing spark plugs and making sure there was at least 40lbs of air in the tires. I even had the traction battery pack tested. Everything checked good. After doing all of these things and spending $455 for the dealer to do a "driveability check" and tune-up, no improvement at all. It wasn't until I did a routine transmission fluid change did I notice a difference. I drained the transmission and examined the fluid. It looked a little darker than normal but didn't look bad. I refilled with 3 1/2 quarts of ATF-WS. The first few days, no noticable improvement. By the end of the first week, MPG had increased to 46.4. The second week, I was astounded when it went to 49.5! I said to myself, if it gets to 50, I'll be satisfied. Now, keeping in mind, this is city/hwy driving, same daily route, same temperatures and same driving conditions. By the end of the third week it became apparent that something had changed. By the end of the tankful it was 52.7 mpg, and has stayed in that range ever since. My advice is, don't wait till the 60, 70 or 80K interval before changing the ATF fluid. Do it every 30,000 miles!
     
  2. Greenteapri

    Greenteapri Active Member

    Joined:
    Nov 19, 2018
    261
    311
    0
    Location:
    Cypress
    Vehicle:
    2013 Prius
    Model:
    Three
    There is no, Toyota prescribed, time to change the cvt fluid, just to 'inspect' it. Instead of going through all the hassle of inspecting it, just change it. Fifty bucks worth of new fluid and an hour of your time is well worth it if you value getting the most out of your Prius.

    Happy to read you're back up to advertised MPG's!

    Have you cleaned your EGR components?
     
    audiodave likes this.
  3. sam spade 2

    sam spade 2 Senior Member

    Joined:
    Mar 31, 2018
    2,178
    991
    0
    Location:
    USA
    Vehicle:
    2017 Prius c
    Model:
    Four
    Good story. The placebo effect is a powerful thing.
    Are you manually calculating your MPG figure......or looking at one of the displays ?
    There is NO good reason to think that your change of fluid actually had anything to do with your improved mileage.
     
    PriusGuy32 and meeder like this.
  4. meeder

    meeder Member

    Joined:
    Jul 8, 2019
    113
    74
    0
    Location:
    Doesburg
    Vehicle:
    Other Hybrid
    Model:
    N/A
    There are so many variables which can influence your mileage that it is extremely hard to pinpoint a source of a change.
    Weather and traffic have a huge impact.
     
    PriusGuy32 likes this.
  5. gliderman

    gliderman Active Member

    Joined:
    Aug 2, 2011
    729
    198
    0
    Location:
    Texas
    Vehicle:
    2010 Prius
    Model:
    IV
    There is no variable in a gearbox, other than normal metal wear. So I doubt that changing the fluid in the "transmission" did anything at all to help your MPG.
     
  6. fuzzy1

    fuzzy1 Senior Member

    Joined:
    Feb 26, 2009
    12,703
    6,263
    90
    Location:
    Western Washington
    Vehicle:
    2012 Prius
    Model:
    Three
    I must agree with the others that this fluid change alone is very unlikely to be the whole cause of the improved MPG. Any MPG loss caused by the old fluid should have been small, if anything at all.
     
  7. Mendel Leisk

    Mendel Leisk Titanic Social Director

    Joined:
    Oct 17, 2010
    35,821
    24,637
    80
    Location:
    Greater Vancouver, British Columbia, Canada
    Vehicle:
    2010 Prius
    Model:
    Touring
    I didn't notice a mpg change after transaxle fluid change, but who knows: if it worked for you, that's what counts. (y)
     
    Ferls80 likes this.
  8. bisco

    bisco cookie crumbler

    Joined:
    May 11, 2005
    83,244
    36,315
    0
    Location:
    boston
    Vehicle:
    2012 Prius Plug-in
    Model:
    Plug-in Base
    maybe someone put the wrong fluid in
     
    Mendel Leisk likes this.
  9. ASRDogman

    ASRDogman Senior Member

    Joined:
    May 29, 2018
    1,378
    876
    0
    Location:
    Indian River County, Florida
    Vehicle:
    2010 Prius
    Model:
    Two
    A few days go the pump I filled up was super slow. It was like filling on the first clip on the handle.
    It took forever to fill the tank. And I wasn't sure if it was really filled, or partially filled. My mpg was 36.
    It should have been around 44mpg. I just figured it was a bad handle.
    Today I filled up at it filled normally. It calculated out to 52mpg. I KNOW that is NOT correct.
    I'm thinking it will go back to normal when I fill up Friday....

    So maybe where you filled up the handle clicked later so more fuel than normal was put in????
     
    PriusGuy32 likes this.
  10. Grit

    Grit Senior Member

    Joined:
    Aug 22, 2017
    2,566
    2,229
    1
    Location:
    BOY
    Vehicle:
    2012 Prius
    Model:
    Four
    I had similar effect. My ATF was changed at our meet ups with the help of raytheeagle, I was able to finish my regular drives home with 4 bars instead of 3 on the HV bat on a consistent basis. Same weather conditions and tire pressure; 44psi on all 4s. Not everyone may yield the same, or similar results. YMMV
     
  11. Mendel Leisk

    Mendel Leisk Titanic Social Director

    Joined:
    Oct 17, 2010
    35,821
    24,637
    80
    Location:
    Greater Vancouver, British Columbia, Canada
    Vehicle:
    2010 Prius
    Model:
    Touring
    Sounds like it over-filled a bit the first time. That would drop your calculated mpg. Then the next fillup was less, due to the previous overfill, which raises you calc'd mpg.

    What this illustrates, is even with variations in fill technique, it invariably balances out over multiple fills.
     
    fuzzy1 likes this.
  12. GrGramps

    GrGramps Active Member

    Joined:
    Jan 15, 2009
    282
    164
    0
    Location:
    Western North Carolina
    Vehicle:
    2012 Prius v wagon
    Model:
    N/A
    Be sure to let us know as it continues to climb.
     
  13. ASRDogman

    ASRDogman Senior Member

    Joined:
    May 29, 2018
    1,378
    876
    0
    Location:
    Indian River County, Florida
    Vehicle:
    2010 Prius
    Model:
    Two
    For some reason, the pump was slow. It just kept going. I was waiting for it to start overflowing, but it didn't.
    It would have kept going, but I decided to stop it.
    I did report it to the state. Nice when they put the phone number on the pump! :)
    I'm sure it will be back to normal on Friday's fill up...

     
    Mendel Leisk likes this.
  14. ALS

    ALS Active Member

    Joined:
    Jul 15, 2009
    554
    252
    0
    Location:
    Pittsburgh
    Vehicle:
    2010 Prius
    Model:
    III
    The disc covering the fuel opening broke on my car a few years ago. If I want I can get another two gallons in the tank after the first click. I have to hold the nozzle in the cup. not inserted in the opening. Most don't realize that speed of the flow, different pump, depth of the nozzle while filling will make a difference in how much fuel you can squeeze in the tank.
     
    ASRDogman likes this.
  15. ASRDogman

    ASRDogman Senior Member

    Joined:
    May 29, 2018
    1,378
    876
    0
    Location:
    Indian River County, Florida
    Vehicle:
    2010 Prius
    Model:
    Two
    Normal fill up today. I figured it would be.
    I know when you fill slow it splashes around a lot so it doesn't completely fill.
    The pump I used has been good, except for the time. Depending on the price, if I stop at
    that station, I will use a different pump. Give them a few weeks to fix it.
     
  16. idohavemail

    idohavemail Junior Member

    Joined:
    Oct 30, 2017
    6
    4
    2
    Location:
    Los Angeles, CA
    Vehicle:
    2011 Prius
    Model:
    Three
    I changed my ATF a couple years ago and my MPG stayed the same in the low-mid 40s. My MPGs are low because I sit in LA traffic... fun times indeed.
     
Loading...