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Sudden drop in MPG

Discussion in 'Gen 3 Prius Fuel Economy' started by aupb11, Dec 8, 2012.

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  1. aupb11

    aupb11 New Member

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    I am hoping someone out there might have an idea what is going wrong with my 2010 prius. I've had it right at 3 years now, and for 65,000 miles I could easily beat 50 mpg per tank. Suddenly, the last 1000 miles I'm down to 41-42, nearly a 20% drop, and the lowest by far I've ever seen with this car! I did just get 4 new tires and they are the Bridgestone Ecopia 422, low rolling resistance tires. I only got one tank in with them on before the plummet in mpg. All other maintenance has been regularly scheduled and taken care of by the dealer, and I've made no modifications at all to the car, and it seems to be running smoothly. A quick search suggests maybe an O2 sensor is bad. Check Engine light has NOT come on. Has anyone run into this issue? Any help is greatly appreciated.

    -I use the tripometer to judge mpg/tank when I get gas
    -tire pressure is 38 all around (same as I used for the old tires)
    -I'm in Alabama and temperatures have been mid 50s at night 70s by day
    -My trips have been in the 300-400 mile range 95% interstate @ 75 mph (as usual)
    -tire alignment is great
    -oil looks great and perfect level
    -I only use ECO mode, in D position
    -AC is used intermittently
    -12v battery test = 12.39v. Not sure what CCA rating is intended, but it was set at 500 and the readout was 436 cca. Temp. 71 degrees. Computer rated it as good but getting low on charge.
     
    #1 aupb11, Dec 8, 2012
  2. cwerdna

    cwerdna Senior Member

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    #2 cwerdna, Dec 9, 2012
  3. cwerdna

    cwerdna Senior Member

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    #3 cwerdna, Dec 9, 2012
  4. Chazz8

    Chazz8 Gadget Lover

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    Check your 12v battery and post in Gen III forum instead of Prius v (wagon) forum. I have read that wiered things can happen when your 12v battery is getting close to the end.
     
    #4 Chazz8, Dec 9, 2012
  5. aupb11

    aupb11 New Member

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    #5 aupb11, Dec 9, 2012
  6. cwerdna

    cwerdna Senior Member

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    You can't. I've already reported it to be moved. It'll likely get deleted or merged w/your other post.

    Out of curiosity, why did you decide to post in the Prius v wagon area?
     
    #6 cwerdna, Dec 9, 2012
  7. aupb11

    aupb11 New Member

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    Just a mistake, I had two windows open and didn't realize I was going to be posting on the wagon area. I guess a capital V would have been more obvious. I thought it was a general care and maintenance section.
     
    #7 aupb11, Dec 9, 2012
  8. cwerdna

    cwerdna Senior Member

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    But that would be even more confusing and wrong.

    The Prius v wagon is supposed to be in lowercase. See Toyota | Toyota Prius v and 2013 Toyota Prius v.

    This is not to be confused w/the 2010 Prius V (uppercase; Roman numeral). See Toyota Vehicles : Toyota Announces Prices for 2010 Prius / Toyota. Toyota switched away from Roman numerals to spelling out the words starting w/model year '11. See MY11 Prius | PriusChat.

    Most of us don't like how Toyota created this confusion which could've been averted by picking some other letter...
     
    #8 cwerdna, Dec 9, 2012
  9. fuzzy1

    fuzzy1 Senior Member

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    Please do answer everything in Cwerdna's questionnaire, to give us as many clues as possible. So far, I'd say that new tires and cooler temperatures and winter fuel blend combined can add up to a serious hit. The tires should improve with age.

    Normally the 12V battery should be not be failing yet, but the 2010s seemed to have been supplied by a bad lot that suffered more early failures than normal. It yours is weak from either the factory or from a few deep drainings, it could also be contributing to low mpg, so check it too.
     
    #9 fuzzy1, Dec 9, 2012
  10. cwerdna

    cwerdna Senior Member

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    ^^^
    OT: Fuzzy1, I noticed you have 888 likes right now. :) That's a lucky # in Chinese culture. :) If you get 1 more, then oh well.
     
    #10 cwerdna, Dec 9, 2012
    fuzzy1 likes this.
  11. fuzzy1

    fuzzy1 Senior Member

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    Maybe if I plead for no more, as DaveinOlyWA did when he wanted to stay at 555, someone will intentionally bump it off that nice number.

    I'm also rapidly approaching 5k posts. Is that a sign of addiction? Will the Likes counteract any addiction problems?
     
    #11 fuzzy1, Dec 9, 2012
  12. JimboPalmer

    JimboPalmer Tsar of all the Rushers

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    I keep trying to get to 1 like for every 4 posts, but I am just not that likable.
     
    #12 JimboPalmer, Dec 9, 2012
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  13. Paradox

    Paradox Prius Enthusiast / Moderator
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    moved and merged
     
    #13 Paradox, Dec 9, 2012
  14. Former Member 68813

    Former Member 68813 Senior Member

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    First, 50MPG @ 75MPG is very good and and almost sounds too good to be true.
    Second, wait for the 422s to break-in. Third, do check the 12V battery. Forth, buy quality top-tier gasoline only and maybe it's time for injector cleaning?
     
    #14 Former Member 68813, Dec 9, 2012
    JMD likes this.
  15. walter Lee

    walter Lee Hypermiling Padawan

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    My 2010 Prius III gets about about 47 mpg @75 mph on Cruise Control if I drive it over 60 minutes
    using Yokohama Avid S33D with the tire pressure set at 40 psi front and 38 psi rear psi.
    with the AC/heater/defroster off, no rain/dry smooth flat road, and the temp about 50 F
    I have 29,000 miles on my 2010 Prius III. If I drop my speed down to about 53 mph I get about 60 mpg when the roads are dry. When the roads are wet and its raining the mpg drops at 55 mph to about 45 to 50 mpg. Bad weather = bad MPGs.
     
    #15 walter Lee, Dec 10, 2012
  16. aupb11

    aupb11 New Member

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    Yes weather is a factor. Unfortunately my drop in mpg has occurred with very mild and dry conditions.
     
    #16 aupb11, Dec 10, 2012
  17. Adam Leibovitch

    Adam Leibovitch Member

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    The 12v battery is another culprit of low mpg on these forums. I replaced mine around 60k miles in a gen2 and got an extra 10% in mpg.
     
    #17 Adam Leibovitch, Dec 10, 2012
  18. fuzzy1

    fuzzy1 Senior Member

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    While the 12V battery is a common trouble spot in Prii, I wouldn't blindly change it without checking it first. Since my first reply, OP edited his post to add this:
    For a Prius, this is perfectly fine.

    The Prius 12V tends to run lower voltage than my non-hybrids, I'll try to find the chart someone else posted.

    PS. Here it is. Numerous Prius drivers were not yet having any battery problems at 11.8-9V, well below the point where my non-hybrids could no longer crank.
     
    #18 fuzzy1, Dec 10, 2012
  19. walter Lee

    walter Lee Hypermiling Padawan

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    I suspect that your drop in fuel efficiency is likely due to a combination of breaking in new tires, the colder temperatures, and the switchover to reformulated wintertime gasoline. The Prius fuel efficiency is very sensitive to the outside temperature and fuel blends ; the Prius' MPGs start to drop as the the outside driving temperature drops lower than 65 F. For example, the colder wetter winter weather and the switch to the wintertime blend gasoline has knocked down the fuel efficiency of my 2010 Toyota Prius by 17% from 71 mpg to 59 mpg in the last few months - a 12 mpg drop.
     
    #19 walter Lee, Dec 11, 2012
  20. aupb11

    aupb11 New Member

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    Toyota 'Health Report:'

    Took it into the dealer and they hooked up their computer, technician said everything was fine. At the bottom of the report are 4 sensor reading, I'm assuming these are the O2 sensors.
    #1=43.5
    #2=38.4
    #3=38.1
    #4=38.8
    Assuming these are the 02 sensors and they adjust the scale to make 43.5=.435 V, from what I can gather online, these are normal readings with the first sensor being about .45v, the second being less than that, and 2-4 being equal. I have no idea what the specifications are for the Prius.

    I'm not doubting the computer reading, however the technician's explanation was a little disturbing. He told me the Prius ran solely off the battery and the ONLY reason for the engine to kick on was to charge the battery. Also, because of the regenerative brakes, a Prius is more efficient in the mountains because of the long downhills (he didn't mention the long uphills).

    Back before the loss in mpg, when I was getting right at 50 mpg each tank, my worst tank of the first 65000 miles with the car was driving through the Rockies, and I still beat 45 mpg, in Power mode. Now I can't get 42 mpg on normal, relatively flat terrain in Eco, and that's going the speed limit and trying to max out mpg.

    I have a bad feeling something is going on, but I'm going to keep on driving.
     
    #20 aupb11, Dec 13, 2012
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