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Lost MPG Fuel Economy 52 MPG down to 36 MPG

Discussion in 'Gen 3 Prius Fuel Economy' started by Reichglass, Sep 9, 2017.

  1. Reichglass

    Reichglass Junior Member

    Joined:
    Feb 4, 2012
    1
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    Location:
    Dallas, TX
    Vehicle:
    2010 Prius
    Model:
    III
    So I had a Dealership say that I should keep the ECO mode on, use non ethanol fuel and the mileage will return. I'm going to call Shenanigans. (I'd use a more colorful word but this is a polite forum HAH!!).
    My car has 244,000 original miles on it. Yes I lived in it. sort of. well taken care of.

    2010 Prius was getting 50-55 MPG until 2 or 2 and a half years ago. Work done in last year to correct.
    (this is aside from regular servicing and tire rotation etc....) mileage first dropped to 45 MPG then 40 MPG the last year and now is getting 35-40 mpg...

    Work Done in last 12 months
    1. Replaced EGR Valve and breather (totally caked up with black gunk)
    2. Recently cleaned the Mass Air Intake sensor
    3. Transmission fluid flush and replace.
    4. Inverter Fluid flush.
    5. 12 V battery replace in last 12 months.
    6. Spark Plugs replaced

    Other symptoms (related? Unrelated?)
    1. MPG drastically reduces while running the are (10-12 MPG loss)
    2. Engine seems to run hot easily while air is on (heat knocking you hear on most small engines while in traffic)
    3. AC Blower Moter has burned out and been replaced 3 times in 3 years.

    Havent tried having the intake manifold(s) cleaned out. Could be a low exit of the exhaust causing bad fuel efficiency? open for ideas.
     
    #1 Reichglass, Sep 9, 2017
    harrysprius and bisco like this.
  2. bisco

    bisco cookie crumbler

    Joined:
    May 11, 2005
    110,132
    50,049
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    Location:
    boston
    Vehicle:
    2012 Prius Plug-in
    Model:
    Plug-in Base
    tyres and pressure?

    check the 12v health, just in case?

    throttle body?

    pcv?

    i have to say, the hvac fan is odd, i wonder if there's an extra load?

    air and cabin filters?

    injectors?
     
    #2 bisco, Sep 9, 2017
  3. Ginto

    Ginto Junior Member

    Joined:
    Jan 23, 2015
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    Vehicle:
    2015 Prius
    Model:
    II
    So I observed the fuel mileage drop and was concerned about the HV battery, I recently had the engine swapped and my mileage jumped from an average of 39 back to 46.5. My EGR valve was swapped under the service bulletin but the cooler was not covered. During the engine swap my mechanic showed me the cooler from my old engine it was a solid carbon wall. (no wonder the check engine light remained on.) They cleaned and installed the cooler that came with the replacement engine.

    You may want to clean the EGR cooler as well as the intake manifold and see if your mileage goes back to normal. Or it could be the gas engine is near the end of life and is just not as efficient as it once was.
     
    #3 Ginto, Sep 17, 2017
    Mendel Leisk and bisco like this.
  4. harrysprius

    harrysprius Active Member

    Joined:
    May 23, 2017
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    126
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    Location:
    Nashville, TN
    Vehicle:
    2010 Prius
    Model:
    V
    It sounds to me like there something dramatically wrong with the AC. Maybe the compressor is starting to go and pulling a high load? Don't forget that it runs when you use the defrost as well, I believe to pull humidity from the air.
     
    #4 harrysprius, Sep 21, 2017
  5. bisco

    bisco cookie crumbler

    Joined:
    May 11, 2005
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    Location:
    boston
    Vehicle:
    2012 Prius Plug-in
    Model:
    Plug-in Base
    rear tyres are probably low.
     
    #5 bisco, Sep 21, 2017
    michael321 likes this.
  6. PriusNeckBeard

    PriusNeckBeard Active Member

    Joined:
    Sep 14, 2016
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    Location:
    Cincinnati
    Vehicle:
    2013 Prius
    Model:
    One
    In to see what the problem was.
     
    #6 PriusNeckBeard, Sep 27, 2017
  7. harrysprius

    harrysprius Active Member

    Joined:
    May 23, 2017
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    Location:
    Nashville, TN
    Vehicle:
    2010 Prius
    Model:
    V
    Any update?
     
    #7 harrysprius, Sep 27, 2017
    Danny3xd likes this.
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