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Gen 4 2017 Prius 4. Gas mileage dropped... why?

Discussion in 'Gen 4 Prius Fuel Economy' started by Wraiththe, Jul 5, 2023.

  1. Wraiththe

    Wraiththe Member

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    Hi
    got a 2017 prius 4 in excellent condition... I think. Tires are good, but my gas mileage average has dropped to 42 MPG. Today it showed as 36.7 MPG for a while and when leaving a parking lot today, it showed 19 MPG
    The slighted activation of the engine or any power seemed to pull the MPG down to the lowest I have ever seen.
    Just go new spark plugs a few weeks ago. I may have the heat exchanger issue, but the coolant levels seem to be fine. Also had both coolants replaced.

    Just had an oil change and they say they check the battery, but I think they are full of sh... at Toyota.

    For reasons I am not going into other than telling me I needed to replace brand new filters... I simply do not trust Toyota anymore. A good mechanic told me to just run chevron gas treatment for fuel injector quality... but I am not sure about that... or if that would effect MPG? All the spark plug heads looked pretty clean when they came out.

    It does seem like the MPG goes down the hotter it is...

    any other suggestions as to why the MPG is dropping? The only other time it dropped, the coolant was low. Right now the reservoir is full.

    When I removed the battery filter, the squirrel fan was spotless... so getting the fans clean seemed unnecessary? Should I take a peek inside? or get an endoscope to see if there are any other fans inside? Can one test the battery without toyota's help?

    lotta questions, sorry.
     
    amos likes this.
  2. bisco

    bisco cookie crumbler

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    mileage?

    are the plugs oem from a dealer?

    how low was the coolant?
     
  3. Doug McC

    Doug McC Active Member

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    Forgive me if you feel I’m stating the obvious (and you probably already know it) but given the warmer weather you are probably running the A/C which is going to result in the ICE running more often (and before any one jumps up and down screaming “the A/C compressor runs off the battery”, I know that!) to recharge the battery. That is going to increase the battery temperature, which is already up due to summer temperatures, and it will result in the ECU relying on the ICE for motive power more often. Thus, fuel efficiency will suffer. If you aren’t running the A/C in ECO mode (which you probably are already), it will help a little bit as will increasing the temperature setting.
     
  4. a2058

    a2058 Junior Member

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    I have a 4 year old Prius, and my mpg is about 8% less than in the first 2 years. I ran the Dr.Prius app and did the battery health test, it’s about 60%. I think as the battery deteriorates or go out of balance, the overall mpg is affected because it’s not able to run on electric as long or as often…
     
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  5. bisco

    bisco cookie crumbler

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    that's a big drop in 4 years, how many miles?
     
  6. a2058

    a2058 Junior Member

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    It’s at 120,000 miles.. it’s doing about 56-57 mpg. Used to do 60-62 mpg back then. Same driving conditions.

    Not yet, but about to change the plugs for the first time coming up when I have some time…

    another curious thing to note was after the first 50000 miles, I changed the transmission fluid and installed a strong, magnetic drain plug in the transmission, from Dimpleplug. This impacted the mpg by about 3-4 mpg consistently… I switched it out to the factory one without the magnet at 100000 miles, the mpg went back up actually. The magnet had quite a bit of metallic residue on it and the fluid was noticeably less dark with the magnetic plug installed. May be the effect of different magnetic field in the transmission affected the motor efficiency…? They may have gone without a magnet on the plug for a reason actually.
     
    #6 a2058, Jul 7, 2023
    Last edited: Jul 7, 2023
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  7. Mendel Leisk

    Mendel Leisk Luddite

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    Yeah could be counterfeit plugs.
     
  8. Leadfoot J. McCoalroller

    Leadfoot J. McCoalroller Senior Member

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    The thing that changes our MPG the most is air conditioning. We can get 60mpg one day and 35 another just down to weather, parking in the sun etc.

    Try some runs with no A/C and see what numbers you get for comparison.

    If you're low on refrigerant, the compressor can overwork to compensate, but that (first) shows up as bad mpg.