Decrease in MPG as car ages?

Discussion in 'Gen 2 Prius Main Forum' started by Kablooie, Jun 6, 2010.

  1. Kablooie

    Kablooie Member

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    My 2004 Prius has 102000 miles and it seems to be getting less MPG. I used to average around 43 and now I'm getting 38 or 39 MPG most of the time.

    Has anyone else experienced this? I'm wondering if the battery loses charge capacity as it ages.
     
  2. macmaster05

    macmaster05 Senor Member

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    whoa. Please advise.
     
  3. mad-dog-one

    mad-dog-one Prius Enthusiast

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    Some people have reported that a failing starter battery (not the traction battery) has this effect. Does your Prius have the original battery?
     
  4. Kablooie

    Kablooie Member

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    Yes. I don't think I've changed the starter battery. It's been 6 years so I'll try replacing it and see if that helps.
     
  5. hobbit

    hobbit Senior Member

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    If anything, my '04 is getting *better* MPG at 130K, esp. as this
    summer kicks in and on the new Michelin EnergySaver a/s tires.
    Finished a run to the Cape and back just today, showing just
    over 70 MPG and much of that was highway at 60+ mph. Traction
    pack is fine, as recently checked, and its 12V is still the
    yellowtop from elearnaid which I don't expect to poop out
    for a good couple more years.
    .
    _H*
     
  6. JimN

    JimN Let the games begin!

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    Before you replace the battery check the voltage & report the readings. For the record, I expect your 6 year old battery to be weak but KNOW why you're swapping out a part, don't GUESS or HOPE that will solve your problem.
     
  7. cwerdna

    cwerdna Senior Member

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    +1

    What tires do you have now (size, make and model please) and what pressures do you keep them at? Perhaps you've changed them to something w/higher rolling resistance?

    Yes, the HV battery does lose capacity over time but government long term tests didn't show significant mileage changes, at least not on Gen Is. See http://priuschat.com/forums/gen-ii-...-miles-w-dropping-mpg-common.html#post1014257.
     
  8. bisco

    bisco cookie crumbler

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    that's excellent H! any tips? we usually get low 60's on the way down and high 50's on the way back. factory tires and 55-65 mph. mostly 65. thanks!
     
  9. Kablooie

    Kablooie Member

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    Good point. I checked and it's 12.5 V cold and 13.75 when idling.
    So the battery seems to still be fairly good. Hmm.

    About a month ago I got new Michelin Energy Saver A/S P185/65R15 all at 35 psi.

    I was getting about this mileage with my previous tires and assumed they could be the problem. When the sidewall of one of them ripped I decided to replace the tires with new energy savers. If anything, the mileage is a little less than before.
     
  10. a_gray_prius

    a_gray_prius Rare Non-Old-Blowhard Priuschat Member

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    When is the last time you checked your alignment?
     
  11. David Beale

    David Beale Senior Member

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    The new tires must "break in" before they will yield good mileage.
    It's time for the spark plugs to be checked/replaced.
    Engine air filter ok?

    The Prius is good at not aging fast, but even it requires maintenance eventually. ;)
     
  12. hobbit

    hobbit Senior Member

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    Very late answer to bisco and anyone else curious: This may help,
    as I hadn't finished writing it at the time the topic came up...
    .
    _H*
     
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  13. LoveMyPriusIII

    LoveMyPriusIII New Member

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    12.5 seems pretty low. I think it is supposed to be 12.8.
     
  14. 2009Prius

    2009Prius A Wimpy DIYer

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  15. NoMoShocks

    NoMoShocks Electrical Engineer

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    I think you need to turn on the headlights and see it that 12.5 V imediately drops below 12 V. I new fully charged battery would be closer to 13.2 V with the car off.
     
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