2010 Prius 45-50 MPG deteriorated to 30 MPG

Discussion in 'Gen 3 Prius Fuel Economy' started by stanzeen, Feb 13, 2015.

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  1. stanzeen

    stanzeen Junior Member

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    I live in Massachusetts, and my 2010 Prius was not breaking MPG records with 45 MPG (max 50) since I bought it 1 3/4 yrs ago, but since November '14, it's steadily declined to 30 MPG or so. Most of my driving is stop-and-go, around town. Only 35K on the odo. It's been brutally cold off & on over the past few wks, but I had a 2006 for 3 years, and it never did worse than 45 mpg even in sub zero temps. I'm envious of all the posters who brag about their 60 mpgs. With all due respect to the cold temps, what am I doing wrong? And how can I get back to my old 'normal' of 45 or 50?
     
    #1 stanzeen, Feb 13, 2015
  2. JC91006

    JC91006 Senior Member

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    It has to do with using the heater........and possibly a weak 12v battery
     
    #2 JC91006, Feb 13, 2015
  3. stanzeen

    stanzeen Junior Member

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    I rarely use the heater, but the 12V battery? I'll have it checked out. I'm sure it's the original battery.
     
    #3 stanzeen, Feb 13, 2015
  4. JC91006

    JC91006 Senior Member

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    I replaced a failing battery on my 2010 v and went from 40mpg to 44mpg.
     
    #4 JC91006, Feb 13, 2015
  5. stanzeen

    stanzeen Junior Member

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    Hmm...well a 10% increase would get me from 30 to 33. Not good enough, but thanks for the feedback.
     
    #5 stanzeen, Feb 13, 2015
  6. JC91006

    JC91006 Senior Member

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    You can also check your tire pressure. The older Gen2 cars are better for intown driving because of their smaller engines. The Gen3 cars are better for highway driving and not as good for intown driving.
     
    #6 JC91006, Feb 13, 2015
  7. stanzeen

    stanzeen Junior Member

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    Thanks, but new tires. All pumped up. Checked today.
     
    #7 stanzeen, Feb 13, 2015
  8. JC91006

    JC91006 Senior Member

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    well the type of tire and also because they are new tires....will also cause a drop in mpg
     
    #8 JC91006, Feb 13, 2015
  9. stanzeen

    stanzeen Junior Member

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    From 45-50 to 30?
     
    #9 stanzeen, Feb 13, 2015
  10. The Electric Me

    The Electric Me Go Speed Go!

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    I changed my 12 volt battery and my Grandmother came out of a coma, my lost dog returned, and that tattoo that I regretted faded away.
     
    #10 The Electric Me, Feb 13, 2015
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  11. Blizzard_Persona

    Blizzard_Persona Senior Member

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    Here is a comparison of my commute in my Persona just to show how a 20 degree drop really affects MPG. Tires set to 44/42.

    First 3 pics are heading in at 6pm, temp is mid 30's, cc @ 55mph, heavy traffic for last few miles. Heater set to windshield defrost for a few mins then shut off totally for remainder of commute.

    last 3 pics are returning at 4am. No traffic, a bitter 12 degrees outside (so approx 20 degree drop), 55 mph on cc, an a <10 min warm up with heater set to auto at 67 while I got changed after work then I set it to 70 (face/feet) at 1 bar fan speed, so very low draw.

    [​IMG]
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    A 30% decreases in MPG due simple to a 20 deg drop in temp....

    I think I found your issue. It's damn cold out, not to mention ain't mass buried under 6' of snow right now. ??


    So if you drive a lot faster than 55.... That might be your issue Mass is def as cold or colder than PA

    Read more: The Persona Project..One Year Later... | Page 5 | PriusChat
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    #11 Blizzard_Persona, Feb 13, 2015
  12. stanzeen

    stanzeen Junior Member

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    Too late for Grandma, but I've missed that dog and have always wondered about getting rid of that "Trixie" tattoo. Mega thanks!!
     
    #12 stanzeen, Feb 13, 2015
  13. stanzeen

    stanzeen Junior Member

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    Whoops - didn't see the rest of your post with the images. But I've been driving Priuses in various conditions for 8 years. We've had some very cold winter spells here. Yes, we've got some deep snow right now, but this loss of MPG is totally new. I rarely go over 55 MPH, so that's not the issue. I'll try the battery. I really miss the dog.
     
    #13 stanzeen, Feb 13, 2015
  14. bisco

    bisco cookie crumbler

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    my biggest winter summer difference was from 65 to 55 in my gen II's. so, about 15% based on temp, heater, winter gas and moisture.
     
    #14 bisco, Feb 13, 2015
  15. Blizzard_Persona

    Blizzard_Persona Senior Member

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    My little test yesterday does show a 30% difference in mpg. Same baseline speed (except for some traffic on the way in)...

    And this is my second prius btw...
     
    #15 Blizzard_Persona, Feb 13, 2015
  16. bisco

    bisco cookie crumbler

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    that's a bigger drop than i've ever seen, but i'm going by tank averages.
     
    #16 bisco, Feb 13, 2015
  17. stanzeen

    stanzeen Junior Member

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    I'm replacing the battery tomorrow. This 30 MPG thing is totally new. I've never had this happen in the past 8 years of Priuses, which never went below 44 MPG in any weather/conditions, including winter driving & ultra cold temps. I will report back after replacing battery and refilling. BTW, I even tried replacing my usual discount gas w Exxon/Mobil the last two refills. I also tried E/M 89 vs 87, and still no difference. So - TBD.
     
    #17 stanzeen, Feb 13, 2015
  18. retired4999

    retired4999 Prius driver since 2005

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    Use 87 gas top tier gas. 89 or higher will not help unless you are in the mountains!
    News reports you are having one of the coldest winters in the last 20 years, and that is a real killer for mpg.
    Now with that being said if your 12 volt battery is 4-5 years old it would be a good thing to check.
     
    #18 retired4999, Feb 13, 2015
  19. bisco

    bisco cookie crumbler

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    we see the same temps, so i don't think it's a bigger issue than usual. could be several things added up. lets see what the new battery brings. the new tyres could be costing you 5 mpg. what kind are they, and did your problems begin sometime after replacing them?
     
    #19 bisco, Feb 13, 2015
  20. Robert Holt

    Robert Holt Senior Member

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    The records for our Gen 3 hatchback indicate a drop from about 54-55 to 49-50, so also about a 10% decrease from summer temps to winter temps in Northern Virginia.
     
    #20 Robert Holt, Feb 13, 2015
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