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

Lower MPG than usual

Discussion in 'Gen 2 Prius Main Forum' started by GeorgeMW, Oct 19, 2019.

  1. GeorgeMW

    GeorgeMW Junior Member

    Joined:
    Sep 11, 2017
    56
    3
    0
    Location:
    Georgia
    Vehicle:
    2007 Prius
    Model:
    N/A
    Hello, my gen 2 has been having lower MPG than usual lately, there are no indications on either screen. I was wondering whether the spark-plugs were doing fine, could busted spark-plugs cause an indication to appear on the screens?
     
  2. bisco

    bisco cookie crumbler

    Joined:
    May 11, 2005
    107,571
    48,862
    0
    Location:
    boston
    Vehicle:
    2012 Prius Plug-in
    Model:
    Plug-in Base
    not likely. could it be the dropping outside temp?
     
  3. bisco

    bisco cookie crumbler

    Joined:
    May 11, 2005
    107,571
    48,862
    0
    Location:
    boston
    Vehicle:
    2012 Prius Plug-in
    Model:
    Plug-in Base
    how many miles on her? have you checked all the usual suspects?

    have you done the prescribed maintenance?
     
  4. PriusCamper

    PriusCamper Senior Member

    Joined:
    Mar 3, 2012
    10,775
    4,372
    0
    Location:
    Pacific Northwest, USA
    Vehicle:
    2007 Prius
    Model:
    Two
    If you had a truck that got 10mpg and then it only got 9mpg it would be barely noticeable... But it you have a Prius and it gets 50mpg and the drops down to 45mpg that would be noticeable. Funny part is both of those differences are the same 10% decline in MPG, its just the the Prius seems like a lot more.

    More to the point, very small subtle things can change gas mileage... Low tire pressure alone can wreak havoc on MPG, but same with cold winter weather using the heater on full blast or hot summer weather with air conditioner on full blast. Ideally, driving 40-50mph in 75-85 degree weather seems to be the sweet spot for the best MPG for Prius.

    Also driving conditions and who you buy gas from is key too. For example my drives to California from the Pacific Northwest shows 43 or MPG in winter in the rain, but then I get to California and buy their more heavily regulated higher quality gas and drive on dryer much newer roads and my MPG shoots up to near 50mpg right away

    So to answer you question, start working on your car and do everything possible to improve gas mileage, do basic maintenance and you'll see a boost. Alos experiment with adding a pound or two PSI at a time in your tires, then once you notice less traction let a little air out. Myself and other prefer a tire in the 45psi range.

    And keep in mind people who are only getting 35mpg in their Prius in many cases don't have anything wrong with their car that needs to be fixed, just lots of little things that need to be further refined.
     
  5. GeorgeMW

    GeorgeMW Junior Member

    Joined:
    Sep 11, 2017
    56
    3
    0
    Location:
    Georgia
    Vehicle:
    2007 Prius
    Model:
    N/A
    Thanks a lot for the info, the hybrid system is quite clean, the temperature is about 25 celsius, and the roads don't exactly allow for more than 36psi. I've got about 100k miles so that's why I thought maybe the spark-plugs were at fault. Is it mandatory to change the spark-plugs at 100k? Rather, would there be an indication somewhere if the spark-plugs were indeed at fault?
     
  6. bisco

    bisco cookie crumbler

    Joined:
    May 11, 2005
    107,571
    48,862
    0
    Location:
    boston
    Vehicle:
    2012 Prius Plug-in
    Model:
    Plug-in Base
    no, you won't get an indication until a check engine light comes on. but plugs are only one possibility at that point.
    toyota recommends changing them at 120k, but if you would feel more comfortable doing them now, the oems are pretty cheap, and the labor is a bit fussy.

    otoh, the sooner you change them, they less likely they will be frozen in place.
     
  7. Graeme1949

    Graeme1949 Member

    Joined:
    Oct 20, 2014
    51
    47
    0
    Location:
    Atlanta, GA
    Vehicle:
    2004 Prius
    Model:
    Two
    The recommended change time for the plugs is, if my memory is right, 120k miles. However, I did not notice that the dealer I was using at that time neglected to change them. A little after 200k miles I was stopped at a traffic light when the engine started sputtering & choking like it was misfiring on 2 or 3 of the cylinders. There was NO OTHER INDICATION OF A PROBLEM. My current dealership was around 200 yards down the street so I got the car there - where the factory plugs were replaced with new ones.

    So, you can probably go more than 120k miles, but I would not recommend trying to push it to 200k.


    (Original owner, 2004 Prius, over 200,000 miles)

    -Graeme-
    2004 Prius with >190,000 miles.
    Sent ?.
     
  8. PriusCamper

    PriusCamper Senior Member

    Joined:
    Mar 3, 2012
    10,775
    4,372
    0
    Location:
    Pacific Northwest, USA
    Vehicle:
    2007 Prius
    Model:
    Two
    I replace my plugs at 120K... It was a waste of time... The plugs still looked almost new even after 120K... These engines run cleaner than anything I've ever seen....
     
  9. srellim234

    srellim234 Senior Member

    Joined:
    Jun 26, 2015
    1,192
    1,680
    0
    Location:
    Laughlin, Nevada
    Vehicle:
    2008 Prius
    Model:
    Touring
    I don't see where you stated how much your mileage actually dropped. Have you physically calculated it over multiple tanks to arrive at your conclusion it's going down?

    Among the "usual suspects" Bisco refers to in Post #3, how old is your 12v battery? That has an affect on a lot of Prius systems but an early sign it's going can be a reduction in mileage.