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Hit a new low in mpg

Discussion in 'Gen 3 Prius Fuel Economy' started by jon55, Jun 25, 2015.

  1. jon55

    jon55 New Member

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    My current tank averages have been dropping for some time. I am consistantly only averaging around 31mpg with no check engine lights or issues. Just doing normal driving. I have the LRR bridgestone tires and use chevron gas regular. any thoughts. average speed of tank is around 25-35 mph. but i drive 70 on the freeway and normal acceleration.
     
  2. JC91006

    JC91006 Senior Member

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    There's someone stealing your gas
     
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  3. bisco

    bisco cookie crumbler

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    have you checked your 12v health. what are your historical mpg averages?
     
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  4. fuzzy1

    fuzzy1 Senior Member

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  5. bisco

    bisco cookie crumbler

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    good point, especially 2010's.
     
  6. fotomoto

    fotomoto Senior Member

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    Could be a combination of several things; tire pressure, brake drag, more a/c use, poor gas, etc
     
  7. jon55

    jon55 New Member

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    i have a 2010 prius base model
    Im getting a tank average of 350 miles.
    i used to get 470
    tires inflated pass max to 40psi max Bridgstone EP22 ULRR
    12v battery is original has good voltage normal range
    terrain has small hills and traffic lights as normal
    oil is checked with everytank of gas and kept beween the two lines I do lose about half a quart between oil changes
    i use 0w20 and all toyota synthetic and toyota filters
    Drive in D mode all the time
    AC is set in auto on 72 at all times
    brakes shake a little from possible warped rotor from a speedy trip down the grapevine while on a roadtrip
    driving style is speedy but nothing above the flow of traffic
     
  8. jon55

    jon55 New Member

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    last 5 tanks have been 320 miles a tank and fill 9.5 gallons roughly
     
  9. fuzzy1

    fuzzy1 Senior Member

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    Tank distances are not very useful to use us because 'tank' means such vastly different things to different people. MPG, either from the display or calculated from the refills, is far more useful.
    ???
    Are they inflated to 40, or to the maximum number listed on the sidewall? I don't recall any common tires with a 40 psi max stamped in the sidewall, most that we deal with show 44 or 51.

    Are the tires original, or new, or replacements that have already rolled more than a couple thousand miles?
    Again, actual numbers please, along with how long since the car was turned off before making the voltage measurement. 'Normal' has too many meanings, and too many shops have reported batteries as being good when they really were not.

    The car could be 6 years old now, so an original 12V battery would be a suspect. Some would still be OK, but many are already dead or dying.
    You could save a bit by pushing the fan speed down, and the temperature up, and likely still find adequate comfort. But this could comprise only a small part of your MPG shortfall.
    You should have switched to 'B', not driven down it in 'D'.
    Can you give us actual speed numbers? 'Flow of traffic' means vastly different speeds in different regions.
     
    #9 fuzzy1, Jun 25, 2015
    Last edited: Jun 26, 2015
  10. bisco

    bisco cookie crumbler

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    how many miles on her? the warped rotors thing is concerning.
     
  11. Mendel Leisk

    Mendel Leisk EGR Fanatic

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    Jon, did you get the software update, to better protect the inverter? There was a recall notice.

    Some owners reported significant mpg drop after the update. Others none. Personally our mpg seemed to improve slightly, post update. Seems a crap shoot, with some owners losing.
     
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  12. jon55

    jon55 New Member

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    just went and double checked everything. yes the tires are set for 40 psi max there the bridgestone ep20... not ep22. The tires have maybe 10k miles tread left so very minimal prob around 40k miles on them. I have not had it into the shop for the software upgrade. i will try and get a new battery for it and see if that helps. id say speed around town is stop and go at 45-50 and freeway is southern california style. im not expecting more than 42mpg but am way off that mark.

    Tank mpg was using the miles driven divided by the gallons added. the mpg reading on my car is 31.8 mpg over the last 6 gallons from the tank. i will try and do some research more on the site and see what i can come up with to help.
     
  13. fuzzy1

    fuzzy1 Senior Member

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    That easily rules out the new tire break-in issue, where new tires reduce mpg a bit until they are broken in.
    Do you have a voltmeter to measure the battery, after the car has been sitting off for at least a few hours, and before re-starting it?

    While aged 12V batteries are a common issue, they are not always part of the problem, some are still good enough at that age. Thus, some folks have replaced it and gained nothing. So it would be useful to get a reading before blindly shotgunning the battery, unless you are ready to just replace it anyway.
    I hadn't looked back at your first post as a reminder, so missed the mpg number.
     
    #13 fuzzy1, Jun 26, 2015
    Last edited: Jun 26, 2015
  14. fotomoto

    fotomoto Senior Member

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    OK, sounds like you've covered most bases (the warp rotors might be culprit) but before attributing it solely to the car, we should try and see if it's the driver and a change in driving habits. So, I'd suggest you top off the tank, give it your best attempt at hypermiling kung fu and report back.
     
  15. bisco

    bisco cookie crumbler

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    some people start having fuel issues, throttle body, injectors and etc., so, you've got a pretty long list of things to check out. start with the easiest, and work your way up. all the best.(y)
     
  16. Mendel Leisk

    Mendel Leisk EGR Fanatic

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    See if any wheels feel hot, after extended drive.
     
  17. earls1

    earls1 New Member

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    I'm curious whether a new ECU I had installed could be causing low mpg due to not being calibrated correctly? I

    have a very confusing situation with my 2006 Gen 2 Prius:
    - 3 month ago Hybrid battery failed, and I had to pay to have a brand new one installed
    -Toyota also installed a new ECU
    - first week, shot up to about 44 mpg
    - Suddenly a few weeks later, plummeted to 27 mpg. I was driving the exact same routes in the exact same manner.
    - Toyota dealer did a diagnostic check on battery and claimed everything was fine.
    -Thanks to the priuschat forum, I noticed that people said when 12v battery is dying they saw a sudden major drop in mpg. I used a simple test and discovered that my 12v battery was indeed shot, which made sense because it was about 5 years old.
    -I replaced the 12v battery
    - Mileage immediately jumped up to around 40 mpg.
    -But again, about a week later it plummeted to 32 mpg. Strangely, my MPG meter on the display jumped around like crazy, even when I drove steady.This is exactly what it did when the HV battery died.
    - I noticed that in the city, when accelerating power is very weak and the gas engine is always running at 100% without any assiatance from the HV battery. On the highway, mileage seems to be ok, in the low 40s. But again, when accelerating or driving lower speeds in the city, it is struggling and powered only by the gas engine.
    -Lastly, HV Battery meter that shows bars to indicate charge, never, ever, reaches a full charge. It's always 3 or 4 bars short. Correct tire pressure, not running AC or high heat.

    I'm wondering if any of these might be the culprit:
    - When Toyota replaced ECU they didn't update software or calibrate it correctly
    - When I removed the old 12v battery and installed new one, it caused ECU to lose correct codes/calibration
    -Toyota gave me a defective ECU
    -

    Any advice is appreciated!
     
  18. Mendel Leisk

    Mendel Leisk EGR Fanatic

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    Just to add to your list of possible culprits:

    - The new battery is marginal/defective? Say due to sitting in storage too long, or whatever? Or (a little paranoid) because it was actually used, or returned, something like that?
     
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