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Trying to understand where my MPG went

Discussion in 'Gen 3 Prius Fuel Economy' started by RootBreaker, Aug 30, 2023.

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  1. RootBreaker

    RootBreaker Member

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    Hopefully this is the right place to post.

    Bought my 2014 prius 3 back in July 2013 and if Covid didnt happen, I would have over 250k miles on it. Due to Covid, I only have 196k... yup only... lol..

    anyway, since I commute 65 miles each way to work mostly highway, I have learned how to "drive" the prius.

    My real numbers are
    Summer @65mph (65+mpg) - 70mph (58-62 mpg) in a 65mph zone
    Winter - since winter gets my mpg down to around 55mpg, I tend to do 70-85mph as I get 55mpg at 70 and 48mpg at 80ish.....

    With that, things have changed. It has been recently happening and not sure why or what to check.
    No engine codes, no hesitation, car runs great on battery, etc.

    I have 50psi in tires and I am struggling to get 50mpg! I just dont get it. I am going to change the air filter but not sure what else to try.

    In actuality, 48mpg isnt anything to shy away from as it is still good; however, 60-65mpg is way better!!!! LOL..
     
    #1 RootBreaker, Aug 30, 2023
  2. sam spade 2

    sam spade 2 Senior Member

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    Have you ever changed the 12 V battery ?
    Have you ever run a dose of Techron through with the gas ?

    I personally think that your 65 MPG at 65 MPH is not an
    accurate number. Are you getting that from the dashboard
    or from doing the math by hand ?

    But with a 10 year old car with that kind of mileage, it is just getting old and tired......so to speak.
    Is it using any oil ?
    Worn rings and a hybrid battery getting weak can cause a drop in efficiency before any
    "trouble" actually shows up.

    P.S. What is the max. pressure shown on the sidewalls of your tires ??
    You should NEVER go over that for safety reasons.
    AND.....excessive pressure might be doing the opposite of what
    you want if it decreases the contact patch of the powered wheels so that more
    slippage occurs where the tire meets the road.
     
    #2 sam spade 2, Aug 30, 2023
  3. fuzzy1

    fuzzy1 Senior Member

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    These MPG vs speed figures are better than what @bwilson4web posted on this once very useful chart, now lost after a series of website host moves and 'upgrades':
    Updated MPG vs MPH chart | PriusChat

    A simplified rule was that the Gen3 could achieve (MPG + MPH) ~= 120.

    Since you were getting closer to 130, I have to wonder if you used to get some significant highway drafting benefit, and are getting less now.
     
    #3 fuzzy1, Aug 30, 2023
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  4. RootBreaker

    RootBreaker Member

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    duplicate post. sorry
     
    #4 RootBreaker, Aug 30, 2023
  5. RootBreaker

    RootBreaker Member

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    The normal car battery? that 12v? errr nope.. havent changed that but it seems strong and that controls lights and the sort. do you think that could do it?


    by hand.. fill up, drive 120 miles, fill up and calculate...

    hmmm i dont check the oil lol. I do my own oil changes every 10k miles and never really see if i get out of it what it should have!
    I do have the dealership do it every 50k so they do the 140pt inspection or whatever it is.. and tire rotate but that price has gone up drastically so not doing that again. was $65 and now $125...

    This is one of those controversial things where some people feel too much pressure you could loose mpg. I have not had that happen and I am on my 3rd set of tires.
    I can tell you I have 50psi and sidewall says 51psi...
    check my old thread out when i got the car. some 60mpg posts... y all time best was 71mpg

    NJ 2014 Prius Three | PriusChat
     
    #5 RootBreaker, Aug 30, 2023
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  6. RootBreaker

    RootBreaker Member

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    just completed 1 day round trip..
    tto work and back. gauge said 54mpg... calculated 120mi /2.25 gallons = 53.3333mpg.

    just put techtron on...
     
    #6 RootBreaker, Aug 30, 2023
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  7. sam spade 2

    sam spade 2 Senior Member

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    Yes. The "normal" 12 V car battery.
    They don't last forever and yours is going on 12 years old now.
    That's roughly TWICE the normal life expectancy.
    And it also runs all of the onboard computers.

    This is a joke, right ??
    No probably not.....but being concerned about your gas mileage but not checking the oil
    is likely to leave you stranded on the side of the road someday when it runs out of oil
    and the engine burns up. Seriously.

    There is no controversy involved.
    With some models of tires it WILL happen.
    And max. pressure is hard on the suspension too.
    YOU have not done any controlled tests to know if it is happening to you or not.



    Please read this post over a couple of times until it sinks in.
    You should fully expect a slight loss of fuel efficiency as a vehicle ages.

    If you intend to keep this car running much longer, you need to
    start treating it like the "senior citizen" that it IS.
     
    #7 sam spade 2, Aug 30, 2023
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  8. douglasjre

    douglasjre Senior Member

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    Your shocks were not designed for tires inflated to 50 psi. Don't. No. Just don't. You don't know what you're doing. If you did you wouldn't be doing this
     
    #8 douglasjre, Aug 30, 2023
  9. Grit

    Grit Senior Member

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    Maybe ac was running? I get mid 60 mpgs and ac will take about 8 to 10 mpgs away, 215,000 mi on the car. My hv battery will get up to 107F with city driving during the simmers but I rather have mid 90F temps reading on hv bat temp
     
    #9 Grit, Aug 31, 2023
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  10. Mendel Leisk

    Mendel Leisk Senior Member

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    You packed in reporting on Fuelly, quite a ways back? Just looking at the link in your signature.
     
    #10 Mendel Leisk, Aug 31, 2023
    Last edited: Aug 31, 2023
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  11. ASRDogman

    ASRDogman Senior Member

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    I doubt running the a/c will effect the mpg by more that 1 or 2.
    If very efficent and it draws very little power from the hybrid battery.
    If you're loosing 10mpg or more, it's not from the compressor.
     
    #11 ASRDogman, Aug 31, 2023
  12. RootBreaker

    RootBreaker Member

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    By the way my comments, replies are not complaints or defensive replies... just serious thoughts as I am trying to figure this out.




    Trust me.. I know that. I usually get 5-6y max out of any other vehicle battery...
    I am not going to just replace it as it is still working. I figure, yes controls onboard computers but I don't think that will cause MPG issues but maybe I am wrong.


    Not a joke. Every car I have ever had, I check the oil but this thing does not leak. I will check it today as I am 6k miles in and as I stated that I do an oil change every 10k miles.

    Interesting thought here as I did change tires recently and do not recall if I was pulling my 60-65mpg right before...

    I have read that max pressure can be hard on suspension and when the car was new I got 45mpg max at ~32-36psi and when i went to max tire psi jumped up 20mpg... having 196k miles on the car now and always having max psi, i have saved a lot of money, have zero suspension issues (as I just had it inspected by the dealership as they did the oil change and inspection 6k miles ago)

    For the controlled tests - will be done next week as I mention this in my closing post remarks.

    I agree that it is getting older and will lose some efficiency but what I am noticing is almost like the mpg gain from the hybrid part is gone. I say that as it seems I get same mpg with eco on or off.. going to test that today.


    Well that is an interesting thing there... much longer... well not sure yet as we are looking at getting rid of it and getting a gas hog of a gmc sierra 3500 at4 with a 6.6L gas engine. Gets 15mpg on highway if I am lucky. Back to that bad MPG and $7k+ gas bill a year. Prius is costing me a LOT LESS!!!!!

    Senior Citizen?? I just hit 50y old this year and I agree... I can still do everything I used to do; however, takes longer, needs more breaks so yeah... maybe the car is just letting me know! :p

    so today's test:
    65mph for 60 miles - cruise set for morning commute and I struggled but got 52mpg. at 50psi

    Next week I will be doing a few test as the weather is supposed to be roughly the same for 3 days...
    65mph at 40psi round trip of 120 miles
    65mph at 45psi round trip of 120 miles
    65mph at 50psi round trip of 120 miles

    I just put techtron in this fillup and might change plugs this weekend.

    would you buy OEM Toyota plugs or would Autozone OEM suffice? I replaced the OEM at 120k miles with Autozone plugs.
     
    #12 RootBreaker, Aug 31, 2023
  13. Mendel Leisk

    Mendel Leisk Senior Member

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    Has the EGR and intake manifold been cleaned?
     
    #13 Mendel Leisk, Aug 31, 2023
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  14. RootBreaker

    RootBreaker Member

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    no.. on my list!
     
    #14 RootBreaker, Aug 31, 2023
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  15. sam spade 2

    sam spade 2 Senior Member

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    You have my thoughts.
    Your replies are argumentative, whether you think so or not.

    You have made some really BAD assumptions and decisions
    but don't seem open to admitting that.
    Like not checking the oil.
    And thinking that a 12 year old battery is still "good".

    Good luck. I quit.
     
    #15 sam spade 2, Aug 31, 2023
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  16. douglasjre

    douglasjre Senior Member

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    What
    What Is your max speed
     
    #16 douglasjre, Aug 31, 2023
  17. Grit

    Grit Senior Member

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    65 mph max, avg 65 mph on highway for 30 min one way commute and some city limit speeds.
     
    #17 Grit, Sep 1, 2023
  18. Leadfoot J. McCoalroller

    Leadfoot J. McCoalroller Senior Member

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    I would use Denso branded plugs. They were the original equipment supplier to Toyota, and that's what comes out of the Toyota boxes when you buy plugs at the Toyota parts counter.

    Autozone sells many brands, including Denso. What did they sell you?

    Spark plugs are heavily counterfeited these days. Best to buy from the Toyota dealer or from a Denso distributor. Amazon and eBay are full of fakes now.
     
    #18 Leadfoot J. McCoalroller, Sep 1, 2023
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  19. ASRDogman

    ASRDogman Senior Member

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    I've been using Bosch from autozone without a problem.
     
    #19 ASRDogman, Sep 1, 2023
  20. RootBreaker

    RootBreaker Member

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    yeah i did and didnt worry bout mileage then. i quit adding fillups so should remove that from my sig.
     
    #20 RootBreaker, Sep 1, 2023
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