1. Attachments are working again! Check out this thread for more details and to report any other bugs.

Why Has MPG Suddenly Dropped on New 2015

Discussion in 'Newbie Forum' started by Earl Warren, Nov 25, 2015.

Tags:
  1. Earl Warren

    Earl Warren New Member

    Joined:
    Nov 25, 2015
    3
    0
    0
    Location:
    Maryland
    Vehicle:
    2015 Prius
    Model:
    Three
    3 week old 2015 Prius. Like all new Prius owners, been obsessively keeping track of mileage. My trip to and from work every day has been between 50 and 52, depending on traffic. Yesterday, the tire pressure warning cam on and, at the same time, mileage dropped to 39-40. Makes sense. Took it to Toyota, they put air in, told me it happened because it suddenly got cold. Warning light went off. Went to work and, yet again, mileage is between 39-40. Have I accidentally pressed some button or reset something. (I have checked and I am in ECO mode, not POWER mode so it's not that.) HELP!
     
  2. vskid3

    vskid3 Active Member

    Joined:
    Jun 23, 2013
    773
    228
    0
    Location:
    Texas
    Vehicle:
    2005 Prius
    How long is your commute? Shorter commutes can get hit pretty hard when the temperature drops. Longer trips help average out the mileage drop from the longer warm up time.
     
  3. Earl Warren

    Earl Warren New Member

    Joined:
    Nov 25, 2015
    3
    0
    0
    Location:
    Maryland
    Vehicle:
    2015 Prius
    Model:
    Three
    My commute is about 25 miles. The reason I noticed, though, is that for the first 2 weeks the mileage was between 50 and 52, and it suddenly changed. I got the air pressure adjusted but that didn't make any difference. This morning I tried it without ECO mode on, and it was exactly the same as with ECO mode on.
     
  4. wjtracy

    wjtracy Senior Member

    Joined:
    Sep 19, 2006
    11,309
    3,586
    1
    Location:
    Northern VA (NoVA)
    Vehicle:
    Other Hybrid
    Model:
    N/A
    Important thing is to make sure you are hand-calc'ing MPG from actual gaso fill-ups. But cold weather is bad for MPG and lucky to get 50 MPG until next spring. Keep in mind short trips get lousy MPG for first 5 minutes, so the proportion of short/long trips makes a big difference each tank. Also speed is big factor if you're getting up to 65+ the MPG drops off.
     
    mpg_numbers_guy likes this.
  5. Fore

    Fore Don't look back!

    Joined:
    Feb 1, 2011
    494
    107
    0
    Vehicle:
    2010 Prius
    Model:
    II
    Weather mix is now in the gas which means lower MPG's!
     
    bisco likes this.
  6. Munpot42

    Munpot42 Senior Member

    Joined:
    Mar 12, 2012
    1,391
    543
    0
    Location:
    Santa Monica, Ca. 90405
    Vehicle:
    Other Hybrid
    Cold weather hurts mileage, there are things like grill blocking and engine block heaters, you can search this site for more info, since you are in Maryland, not Minnesota, I'd just live with it and look forward to spring.
     
  7. The Electric Me

    The Electric Me Go Speed Go!

    Joined:
    May 22, 2009
    9,083
    5,795
    0
    Location:
    Undisclosed Location
    Vehicle:
    Other Non-Hybrid
    Model:
    N/A
    Hmm....
    I would recommend buying a Tire Pressure Gauge....a good one, is a great investment.
    Check the pressure yourself.
    You really don't want the TPMS while you are driving being the indicator for you. I think of TPMS as a fail safe, we have a problem, indicator, not as a maintenance reminder.

    I'm suspicious that you may have a problem with your tire(s) or rims. Outside temperature does affect tire pressure, but in my experience usually not so rapidly or extremely as to cause the TPMS to alert.

    You've ONLY owned the vehicle for weeks. So it is possible the tires weren't inflated to the right PSI since driving off the lot.
    When I bought my new Prius, the tires were for some reason -way over inflated.

    It may be that everything is OK now.

    But one first step and a good thing to do anyway is own and have a Tire Pressure gauge, and periodically check the PSI yourself.

    As far as MPG? I wouldn't panic. Just reset at next fill up and keep an eye open.
     
    Mendel Leisk likes this.
  8. fuzzy1

    fuzzy1 Senior Member

    Joined:
    Feb 26, 2009
    17,036
    10,011
    90
    Location:
    Western Washington
    Vehicle:
    Other Hybrid
    Model:
    N/A
    By the time the tire pressure warning lights up, the pressure is much too low for MPG and tire life. Regular shop visits are too far apart, don't wait that long, get a pressure gauge and maintain the pressure yourself.. If someone else's air supply (e.g. gas station) is not convenient, then get a small 12V air compressor or bicycle pump (full size floor model, not compact hand-held model) so you can top off the tires at home.
    A helpful thread about winter MPG:
    Why mileage gets worse in winter | PriusChat

    A questionnaire to supply us with more clues if your MPG is below expectations:
    Fuel economy complaints/queries? Please copy, paste & answer these questions, esp. if you're new | PriusChat
     
  9. bisco

    bisco cookie crumbler

    Joined:
    May 11, 2005
    107,571
    48,862
    0
    Location:
    boston
    Vehicle:
    2012 Prius Plug-in
    Model:
    Plug-in Base
    unfortunately, the only good measurement is long term gas tank fill ups. don't bother with your average reading screen. report back here every time you fill up. perhaps we can be of help.
     
  10. Earl Warren

    Earl Warren New Member

    Joined:
    Nov 25, 2015
    3
    0
    0
    Location:
    Maryland
    Vehicle:
    2015 Prius
    Model:
    Three
    Okay -- here are the answers to the questionnaire!

    - Have you read This Thread Yet? Yes.

    - What fuel economy are you getting and how are you determining fuel economy? Trip computer.

    - What fuel economy are you expecting and why? 50-52, because (1) it’s what I was told I would get, and (2) because it’s what I got until this week – with identical driving conditions. Suddenly, this week, it went down to 40.

    - What are the approximate outside air temps? 45.

    - How long are your trips? 30 miles.

    - How old is your 12v battery? What is the voltage reading of your 12v battery after sitting over night? Brand new.

    - Have you had your alignment checked? Any pulling or abnormal tire wear? No pulling, new tires, no wear, car is 3 weeks old.

    - How much of it is city vs. highway? Roughly what's the average speed in overall and of each segment? Is there a lot of stop and go driving? My 30 mile commute, each way, is mostly country, a few stoplights, I’m generally at about 55 and use the cruise control so I know it’s steady.

    - What's the terrain like of your drives? Pretty flat – I live in a tidal wetland!

    - What are your tire pressures? Don’t know, but the dealership adjusted the pressure 3 days ago.

    - Is your oil overfilled? Nope.

    - Make, model, year, engine and transmission of previous car? What did you actually get on the same trips/commute? 2005 Camry. About 30 MPG.

    - What region/state are you in? Southern Maryland.

    - How are you trying to drive and how hard are you braking? Trying to stay in ECO, not electric only. Trying to brake gradually like I was told in order to charge the hybrid battery.

    - What modes are you using, if any? ECO.

    - Are you "warming up" the ICE by letting it idle after powering on? Not usually.

    - Are you driving using D or B mode? D.

    - HVAC settings? I’ve been leaving it off since my MPG suddenly got so much lower.

    - Are you using the factory tires and wheels? Factory.

    - If reporting a mileage drop, did anything significant change on your car or your commute? Nothing significant. My tire pressure gauge came on and I took it to the dealer, who told me it was because the weather had gotten colder, and he adjusted the pressure and the light went off. The mileage did not go back up.

    For the first 2 weeks it was steady at 50-52 MPG. For the past week it has been steady at about 40 MPG.
     
  11. Mendel Leisk

    Mendel Leisk Senior Member

    Joined:
    Oct 17, 2010
    54,474
    38,105
    80
    Location:
    Greater Vancouver, British Columbia, Canada
    Vehicle:
    2010 Prius
    Model:
    Touring
    One possible scenario: the dealership goofed off on the pre-delivery inspection. When cars leave the factory they set the tires at the max pressure indicated on the sidewall, to avoid flat spots during prolonged sitting around. During the PDI the dealership is supposed to set the pressures to the recommended pressure, as indicated in the driver's door decal. And reset the TPMS system, to acquaint it to those new values.

    If they didn't do that, you drove for a few weeks, lost a bit of pressure with falling temperatures, the TPMS warning went off, they checked it they realized their oversight, and set your pressures a lot lower, per the decal, and reset the TPMS. And this lowering of pressure is lowering your mpg.

    May be, or not, just my thought.
     
    mpg_numbers_guy likes this.
  12. fuzzy1

    fuzzy1 Senior Member

    Joined:
    Feb 26, 2009
    17,036
    10,011
    90
    Location:
    Western Washington
    Vehicle:
    Other Hybrid
    Model:
    N/A
    I'm not seeing much in here.

    Re-ordering the items a bit:
    MPG always falls in winter, for a variety of reasons. But as you started driving this just three weeks ago, you should have already been in semi-winter conditions from the start. 45F should lower MPG a bit, but not all that much.

    One exception could be the initial fuel supply in the tank. If it was previously filled with summer gas (higher energy density and better mpg), you might see the seasonal blend difference starting from your very first refill. Winter gas was already out before you acquired this car. If somehow it was initially stocked with non-RFG fuel before arriving at your dealer, and you live in an RFG area, this could exacerbate the first-tank difference.

    Have you reset the (or a) trip meter since the tires were aired up? If not, do so now, as the previous history is holding the reading down and slowing its return to normal.

    I use one trip meter to show tank MPG, and the other to show daily MPG. The later provides faster feedback about changes, unburdened by history from yesterday. It also helps highlight the high cost of short trips and engine warmup, the meter starts out abysmally low but climbs throughout the morning commute.
    Falling temperatures do cause some pressure drop, but only about 1 psi per 10F. If your tire(s) fell enough to trigger the TPMS warning, then something else contributed to air loss. (Or the car was delivered with very low pressure in the first place.) Get your own gauge and start monitoring the pressure on your own. I am suspecting a slow leak.

    Some other folks do suffer the same cold weather TPMS warning you received, but they have not checked their tires in 6 to 12 months and suffered just ordinary air loss. This should not have happened in just three weeks without some leak.

    Just FWIW, braking gradually as you were told does recycle some of the braking loss into the battery, but is not the primary source of battery energy. The bulk comes from the engine, spinning MG1.

    ECO vs PWR vs Normal mode is mostly a matter of personal preference, and should make only a small difference, not large. While most of us will do better in ECO, some do better in another mode, and some find no difference (apart from some climate control and cruise control adjustments). A driver with superhuman patience and dexterity should fall into the later category (i.e. no difference). However, most of us are less than superhuman, but with different mixtures of faults. Go ahead and play with the various modes.
     
    #12 fuzzy1, Nov 25, 2015
    Last edited: Nov 25, 2015
  13. fuzzy1

    fuzzy1 Senior Member

    Joined:
    Feb 26, 2009
    17,036
    10,011
    90
    Location:
    Western Washington
    Vehicle:
    Other Hybrid
    Model:
    N/A
    I'm going to doubt that as the sole reason for the initial TPMS warning, I'm still suspecting another contributor such as a slow leak in at least one tire.

    But otherwise, that general scenario would help explain a good chunk of the post-visit MPG loss. Both my Prii were delivered with 40-ish psi, not lowered to the door placard level. And numerous other readers here have reported the same.
     
  14. Lucifer

    Lucifer Senior Member

    Joined:
    Aug 23, 2015
    1,014
    485
    0
    Location:
    Nh
    Vehicle:
    2017 Prius Prime
    Model:
    Plug-in Advanced
    Chances are the dealer had it in ready mode for an hour or two and now the "accumulatve" mileage is showing that fact. Reset the trip meter on the next fill up.
     
  15. Marcius

    Marcius Junior Member

    Joined:
    Jun 28, 2020
    68
    12
    2
    Location:
    So Cal
    Vehicle:
    2017 Prius
    Model:
    Three Touring
    Just wondering if you ever got the problem solved?
     
  16. Prodigyplace

    Prodigyplace Senior Member

    Joined:
    Nov 1, 2016
    11,696
    11,317
    0
    Location:
    Central Virginia
    Vehicle:
    2017 Prius
    Model:
    Two
    Just wondering why you resurrected an old thread and asked a question of somebody who has not been seen here in over 4.5 years.
     
  17. Mendel Leisk

    Mendel Leisk Senior Member

    Joined:
    Oct 17, 2010
    54,474
    38,105
    80
    Location:
    Greater Vancouver, British Columbia, Canada
    Vehicle:
    2010 Prius
    Model:
    Touring
    Just a thought: at the factory they might set the TPMS with door decal pressures, then raise the pressures for shipping. Save the dealer a chore.
     
  18. fuzzy1

    fuzzy1 Senior Member

    Joined:
    Feb 26, 2009
    17,036
    10,011
    90
    Location:
    Western Washington
    Vehicle:
    Other Hybrid
    Model:
    N/A
    Probably because he is a newbie, with a related issue, but has not been here long enough to remember to check posting dates, or to have learned how to check when other posters last visited.

    There is still some potential value in tweaking other members here to respond.