Welcome to PriusChat

We'd love to have you join our community and participate in the conversation! Sign up for FREE today.

Sign Up

Changed my oil and MPG went from 53 down to 46. WTF??

Discussion in 'Gen II Prius Fuel Economy' started by mike52474, Feb 26, 2012.

Social Buttons

  1. mike52474

    mike52474 New Member

    Joined:
    Jan 6, 2012
    Messages:
    29
    Likes Received:
    2
    Location:
    bellbrook,oh
    Your Vehicle Year:
    2008 Prius
    Model:
    N/A
    Hi, there friends, I need some help please. My prius is a 2008 with 60k miles. I just changed my oil and filter today and noticed a drastic drop from 53 down to 46mpg. I used castrol gtx 5w-30 and a mobil 1 m1 103 oil filter. my oil level seems to be fine, the temperatures here are a steady 45f. I double checked to make sure the foot pedal parking brake is all the way released (I set it while I had the car jacked up) My tire pressure is normal. The decrease in mpg happened right after the service I performed. I also reset the "maintenence required" light by holding down the trip reset and hitting the power button twice like you're supposed to do. This is all I did and I think I included all the details for you. It almost felt like the electric wasnt "helping" as much right after the change. This is why I started paying close attention to the info screen to see what my mpg was doing and it def. took a hit. So what do you all think? This is driving me nuts. Thanks so much for your time and info:)
  2. bisco

    bisco cookie crumbler

    Joined:
    May 11, 2005
    Messages:
    19,925
    Likes Received:
    3,222
    Location:
    boston
    Your Vehicle Year:
    2012 Prius Plug-in
    Model:
    Plug-in Base
    how are you calculating mpg's before and after?
  3. mike52474

    mike52474 New Member

    Joined:
    Jan 6, 2012
    Messages:
    29
    Likes Received:
    2
    Location:
    bellbrook,oh
    Your Vehicle Year:
    2008 Prius
    Model:
    N/A
    just watching my info screen where the yellow bar graph is
  4. DetPrius

    DetPrius Active Member

    Joined:
    Apr 24, 2009
    Messages:
    540
    Likes Received:
    86
    Location:
    Southeast Michigan
    Your Vehicle Year:
    2010 Prius
    Model:
    III
    Your observation is after how many miles traveled since the service?
  5. mike52474

    mike52474 New Member

    Joined:
    Jan 6, 2012
    Messages:
    29
    Likes Received:
    2
    Location:
    bellbrook,oh
    Your Vehicle Year:
    2008 Prius
    Model:
    N/A
  6. pwlcheng

    pwlcheng New Member

    Joined:
    Apr 16, 2008
    Messages:
    14
    Likes Received:
    5
    Location:
    Tampa, FL
    Your Vehicle Year:
    2012 Prius
    Model:
    Three


    Try lower the oil level and be sure it is not all the way at the full line.
    Also try tire pressure Front 42 and Back 40
  7. bisco

    bisco cookie crumbler

    Joined:
    May 11, 2005
    Messages:
    19,925
    Likes Received:
    3,222
    Location:
    boston
    Your Vehicle Year:
    2012 Prius Plug-in
    Model:
    Plug-in Base
    i think you need a fresh tank and see what the long term is. pretty tough to judge by driving around and watching the screen.
  8. mike52474

    mike52474 New Member

    Joined:
    Jan 6, 2012
    Messages:
    29
    Likes Received:
    2
    Location:
    bellbrook,oh
    Your Vehicle Year:
    2008 Prius
    Model:
    N/A
    Actually, the oil level is a hair OVER the full dot. Could this really affect the mpg this much? I put a little more than 3.75 quarts in the car. Also, is there an easy way to let out just a little oil?
  9. SageBrush

    SageBrush Senior Member

    Joined:
    Jun 4, 2008
    Messages:
    9,435
    Likes Received:
    1,826
    Location:
    Southwest Colorado
    Your Vehicle Year:
    2012 Prius v wagon
    Model:
    Two
    Give it a day, wtf
  10. bisco

    bisco cookie crumbler

    Joined:
    May 11, 2005
    Messages:
    19,925
    Likes Received:
    3,222
    Location:
    boston
    Your Vehicle Year:
    2012 Prius Plug-in
    Model:
    Plug-in Base


    some say it can, but my guy always puts in what the manual says. it's always a quarter inch over the full mark and i always get the same 55-65 mpg.:rolleyes:
    1 person likes this.
  11. mike52474

    mike52474 New Member

    Joined:
    Jan 6, 2012
    Messages:
    29
    Likes Received:
    2
    Location:
    bellbrook,oh
    Your Vehicle Year:
    2008 Prius
    Model:
    N/A
    Yeah ill def give it a few days:) I hopefully just jumped the gun a bit
  12. Bojan Lalic

    Bojan Lalic New Member

    Joined:
    Feb 11, 2012
    Messages:
    14
    Likes Received:
    5
    Location:
    Macedonia
    Your Vehicle Year:
    2006 Prius
    Model:
    N/A
    From my overall experience with gasoline engines, the best oil level is halfway the Empty and Middle marks.
  13. uart

    uart Senior Member

    Joined:
    Sep 7, 2009
    Messages:
    3,634
    Likes Received:
    763
    Location:
    Australia
    Your Vehicle Year:
    2005 Prius
    Model:
    N/A




    I usually try to fill just a shade under the full dot (1/8" to 1/4" under), as personally I like it to be at least somewhere near full.

    When the Toyota dealer was doing the servicing however then, like bisco, it was routinely 1/8" to 1/4" inch over the dot.

    There may be a really small fuel efficiency benefit to running the oil somewhat under the full dot, but as far as I can tell it's only small. I've been getting 53 to 55 MPG the whole time.

    There does however seem to be a point, that if you overfill past, then there really is a noticeable deterioration in FE. I've never been there, but from what others have reported here it seems to start somewhere between 1/4" and 1/2" over the full dot. Remember that if you overfill then you can get frothing of the oil, giving rise to faster initial oil consumption and excess oil drawn into the intake (which can cause other ongoing problems and reduce FE).
  14. Britprius

    Britprius Senior Member

    Joined:
    Jun 14, 2010
    Messages:
    4,007
    Likes Received:
    1,134
    Location:
    Herefordshire England
    Your Vehicle Year:
    2008 Prius
    Model:
    N/A
    Just a shot in the dark here are you sure the oil was 5w3o and not 20w50 or other heavy oil, probably not but worth checking.
  15. mike52474

    mike52474 New Member

    Joined:
    Jan 6, 2012
    Messages:
    29
    Likes Received:
    2
    Location:
    bellbrook,oh
    Your Vehicle Year:
    2008 Prius
    Model:
    N/A
    Ok guys here is what it was.... I hope this helps others who have seemed to notice this change after an oil change. After I reset the "maintenence required" light I did not reset the trip odometer a and b. You need to reset these to zero also. Also reset the mileage on the big screen in the middle on the "consumption" screen. So, I'm sure my actual mpg never went down. The conflicting info was causing all of the averages to be way off. You must reset it ALL:) I hope this helps. Upon doing this my averages went back to normal. Thanks to all of you for the input!
    1 person likes this.
  16. theorist

    theorist New Member

    Joined:
    Jan 9, 2006
    Messages:
    358
    Likes Received:
    8
    Location:
    Lexington, MA


    I never noticed this, and I changed the oil on our 2006 Prius for the 16th time yesterday (16th time on that car, not all in the same day =). It's nice to hear about new findings from new members.
  17. Cooker

    Cooker Junior Member

    Joined:
    Feb 29, 2012
    Messages:
    29
    Likes Received:
    1
    Location:
    Grand Rapids, MI
    Your Vehicle Year:
    2005 Prius
    Model:
    II
    Why in the world would the trip odometers have anything to do with computed mileage????
  18. uart

    uart Senior Member

    Joined:
    Sep 7, 2009
    Messages:
    3,634
    Likes Received:
    763
    Location:
    Australia
    Your Vehicle Year:
    2005 Prius
    Model:
    N/A


    ^ It doesn't



    ^ This.
  19. Jimbo69ny

    Jimbo69ny Active Member

    Joined:
    Feb 27, 2012
    Messages:
    639
    Likes Received:
    85
    Location:
    Ithaca, NY
    Your Vehicle Year:
    2012 Prius Plug-in
    Model:
    Plug-in Advanced


    Uart is correct. The odometer cannot possibly be the problem.

    However this should be a reminder to everyone NOT to over fill their engine with oil.

    I my oil was 25% over the full line and my mpgs were around 40. I had it dropped to just under full when I put my summer tires back on and I am now at 55 mpg after around 70 miles.

    Granted a large part of the increase was probably found by going back to summer tires but Im sure the oil was part of that. 15 mpg increase is pretty high for it to be just tires.
  20. Cory151

    Cory151 Junior Member

    Joined:
    Mar 3, 2012
    Messages:
    48
    Likes Received:
    14
    Location:
    San Diego
    Your Vehicle Year:
    2005 Prius
    Model:
    Two


    I agree with this, it causes additional crank windage. .
Similar Threads: Changed went
Forum Title Date
Prius v Care, Maintenance and Troubleshooting Changed cabin filter, found mouse nest! Jul 18, 2014
Gen III 2010+ Prius Accessories and Modifications Has anyone changed the color of the foot well lights/floor lights...? Jul 2, 2014
Prius v Care, Maintenance and Troubleshooting Just changed transaxle fluid Jun 30, 2014
Gen II Prius Technical Discussion Has Toyata Core Charge Changed? Jun 23, 2014
Gen III 2010+ Prius Fuel Economy Have your driving habits changed? May 25, 2014