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2017 Prius Prime MPG Decreased by 9-10MPG

Discussion in 'Prime Fuel Economy & EV Range' started by iambozo, Sep 12, 2020.

  1. iambozo

    iambozo New Member

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    Hi Everyone,

    I have a 2017 Prius Prime Premium with about 51k miles.
    Bought it brand new November 2017.
    I was consistently averaging about 53mpg or 530miles a full tank for the first 1.5 years of ownership.
    Now it's down to like 44/45mpg or 440-450miles with a full tank.
    I only drive the car in HV mode, I never charge it. I also live in the Bay Area so it does not get too cold.
    I've been changing the engine oil with Mobil-1 Full Synthetic 0W-20.
    Tire pressure is normal.
    No change in driving behavior.
    ECO-NORMAL-POWER mode seems to make minor changes in mpg.
    Is my hybrid battery degrading that fast?
    I read a thread that someone changed their 12v battery and it improved their mpg ? I'm out of ideas.
     
    #1 iambozo, Sep 12, 2020
  2. bisco

    bisco cookie crumbler

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    original tires?

    have you checked/cleaned/replaced engine and cabin fiters?

    is the oil level correct?

    could the e brake, or regular brakes be dragging?
     
    #2 bisco, Sep 12, 2020
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  3. vvillovv

    vvillovv Senior Member

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    How often do you plug in?
    what is your available EV range when you start the car?
     
    #3 vvillovv, Sep 13, 2020
  4. iambozo

    iambozo New Member

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    Engine and Cabin filters were replaced but still the same.

    Oil levels are correct.

    How do i check if the e-brake or regular brakes are dragging?
     
    #4 iambozo, Sep 13, 2020
  5. iambozo

    iambozo New Member

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    Never charged the car before. Bought the prime soley for the HOV sticker for my commute.
     
    #5 iambozo, Sep 13, 2020
  6. jerrymildred

    jerrymildred Senior Member

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    Already answered.

    @bisco made some good suggestions to get you started.
    The 12V battery could be partly to blame, but it's still fairly new, especially in a climate as mild as yours. But with all the soot you probably have in your air lately, I'd take a look at the engine and cabin air filters first. Then move on to tire pressures, dragging brakes, alignment, dirty MAF sensor, etc.
     
    #6 jerrymildred, Sep 13, 2020
  7. vvillovv

    vvillovv Senior Member

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    I guess you missed what I'm looking for.
    How much of the traction pack is getting used? ie What are the EV estimated Miles every time the car is started.
    If the car has not been charged much it might be an interesting experience if it gets fully charged.
     
    #7 vvillovv, Sep 13, 2020
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  8. bisco

    bisco cookie crumbler

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    put her in neutral around 20 mph on a flat road and see if she free wheels well.

    take her out for some high speed driving, then feel all 4 wheels. is one hotter than the others?
     
    #8 bisco, Sep 13, 2020
  9. iambozo

    iambozo New Member

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    I'm due for a maintenance soon so i'll be changing the following:
    -Oil change
    -Engine & Cabin Filters (Second time replacing these. First set was replaced at 30k miles along with the tires)
    -Clean MAF sensor (i think this may be the culprit due to the yearly California fires)

    -Check for dragging brakes (If this is the cause, how do i fix it?)

    If none of these are the culprit then i guess the next steps would be:
    -Replace 12V Battery

    -Replace tires
    -Alignment
     
    #9 iambozo, Sep 13, 2020
    Tips and bisco like this.
  10. vvillovv

    vvillovv Senior Member

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    how do I fix it?
    Again, it depends on what the issue is with the brakes if there is one....
    If you are having these services done by someone other than yourself you ask to have them done.
     
    #10 vvillovv, Sep 14, 2020
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  11. pghyndman

    pghyndman Active Member

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    Sorry if this is too simplistic, but it does need asking since you do have about 51K miles on the car... did you replace the tires with ones haviing higher rolling resistance?
     
    #11 pghyndman, Sep 14, 2020
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  12. route246

    route246 Member

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    I also live in the Bay Area and I can tell you exactly what happened to me and you can see if it makes any sense. Most of the gas around here is E0-E15. E0 has about 15-20% more thermal potential in it per volume. As soon as COVID became known the ethanol started getting diverted to hand sanitizer and there was none around at the gas pump. Mileage efficiency increased 10%-15% without doing anything. I noticed the odor at the tank smelled more like gasoline and less like ethanol, too. I didn't change my driving habits, either.

    I noticed last weekend the gas I filled up had that ethanol smell again. I burn a lot of gas in my weekend driver (not a Prius). At the same time you may have noticed that hand sanitizer and alcohol is more readily available around here, too. I don't think it is a coincidence.
     
    #12 route246, Sep 15, 2020
  13. Salamander_King

    Salamander_King Senior Member

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    +1

    It seems the first 1.5 years was with the OEM tires, and next 1.5 years must be the new set of tires you changed at 30K. What tires did your have as OEM, and what tires did you get as replacements?
     
    #13 Salamander_King, Sep 15, 2020
    Last edited: Sep 15, 2020
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  14. iambozo

    iambozo New Member

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    Did some maintenance on my prius today:

    Changed oil with Mobil 1 Full Synethic 0W-20.
    Cleaned MAF sensor
    Replaced Cabin filter and engine filter.
    Drove on the freeway for about 15miles, MPG is about the same 47.

    I replaced all 4 of my OEM (Dunlop Enasave?) tires with the same one.

    I think I will be replacing my 12V battery as the next step.
     
    #14 iambozo, Sep 16, 2020
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  15. MikeDee

    MikeDee Senior Member

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    I would get the battery tested by the dealership (assuming they do a load test; you can check the unloaded voltage yourself with a multimeter) before buying a new battery.
     
    #15 MikeDee, Oct 12, 2020
  16. Mistrall22

    Mistrall22 Junior Member

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    Check your brake. Maybe they offer too much friction if the calipers do not move as freely as they should

    Posted via the PriusChat mobile app.
     
    #16 Mistrall22, Feb 18, 2021
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