Consistently getting 35-37 mpg, nothing higher

Discussion in 'Gen 2 Prius Fuel Economy' started by guod, Apr 16, 2012.

  1. guod

    guod New Member

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    I have a 2004 prius with 149k on it and can't seem to break into the 40 mpg range. I live in an area with some hills, but nothing too crazy. I have even had trips of 60+ miles on pretty flat freeways/highways/roads and have only hit 38mpg driving with a very light foot, coasting down hills, coasting to stoplights and using cruise control. I have tried keeping my speeds low and just cant get great gas mileage. I am not sure what else to try.

    In the past few weeks I have had the oil, transaxle and inverter coolant changed and the waterpump was changed 15k ago. I also had the spark plugs changed, air filter and have new tires.

    Does anyone have any clue as to what could be wrong or what I am doing wrong? Could it be my batteries?


    btw, I bought the car used a few months back and have been getting the same mileage since I got it. I have not noticed any improvement from any of the maintenance I have done.


    Here is the Survey
    - What fuel economy are you getting and how are you determining fuel economy? (trip computer or manual calculations)
    35-37 I am doing it via math and via the trip computer

    - What fuel economy are you expecting and why?
    40+

    - What are the approximate outside air temps?

    70s

    - How long are your trips?
    Mostly 15-20 mins with many 30 min to 1 hr

    - How much of it is city vs. highway? Roughly what's the average speed in overall and and of each segment? Is there a lot of stop and go driving?

    70/30 between city and freeway. City=30-55 mph Freeway=65-75 cruise control. Stop and go in city and free flowing on freeway

    - What region/state are you in? (if you haven't set your location in your profile)

    Los Angeles, California,

    - What's the terrain like of your drives? (e.g. flat, gentle hills, steep hills, etc.)

    Gentle hills, flat with a few steep hills

    - Is your oil overfilled? (i.e. above the full mark on the dipstick)

    No

    How old is your 12v battery? What is the voltage reading of your 12v battery after sitting over night? (Method Here)

    One year

    Have you had your alignment checked? Any pulling or abnormal tire wear?

    Yes, had an alignment done recently

    - Are you using the factory tires and wheels? If not, please indicate tire make, model and size (e.g. Goodyear Assurance Fuel Max 185/65R15).

    Stock rims, Doral SDL 65

    - What are your tire pressures?

    38 all round

    - Make, model, year, engine and transmission of previous car? (e.g. 08 Honda Civic Si 2.0L 4 cylinder, manual transmission) What did you actually get on the same trips/commute? (Please give us actual numbers, not EPA ratings.)
    2001 Lexus IS300. I got 17mpg with HARD driving

    - How are you trying to drive (e.g. trying to stay in electric only?) and how hard are you braking?

    I am trying to drive it for best fuel economy. Not racing, coasting most of the time. Normal brakes

    - Are you "warming up" the ICE (internal combustion engine) by letting it idle after powering on?

    Yes

    - Are you driving using D or B mode?

    D

    - HVAC settings? Are you using the heater, AC, auto mode, etc.? If using auto, what temp is it set to?

    Very little AC, sometimes heater
     
  2. jbrad4

    jbrad4 Active Member

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    What is your tire pressure?
    As others on PriusChat have suggested, I have mine set to 44 lbs front / 42 lbs rear.
    You say you recently put new tires on. You normally take a hit on your MPG until you've driven a while on new tires.
     
  3. uart

    uart Senior Member

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    Sounds like you should be doing a lot better than 38. Given the type of trips and temperature I would have thought something closer to 50MPG.

    Most people will say don't warm up the prius it only wastes fuel. A short warm up of 30 to 45 seconds however doesn't give any measurable loss, and personally I find it useful for maintaining good traction battery charge in the first few minutes of a trip.

    This only thing that really looks sus are the tires. If you're interested in fuel economy then why on earth did you buy the cheapest non-LRR rubber you could find? Tires are one of the single biggest things to impact fuel economy. All that being said though, I doubt the tires would account for more than about 5MPG so I'd still expect a little more.
     
  4. guod

    guod New Member

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    yeah, my warm ups are not long at all. I would say under a minute so I do not think that is the culprit.


    I did not buy the tires. they came with the car. I was a little put off by that, but hey, the other guy paid for them so I cannot complain too much.

    Yeah i know that they are not LRR, but I figured even if it gave me 5mpg like you are saying, I am still not where I should be in terms of MPG
     
  5. bisco

    bisco cookie crumbler

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    double check the 12v battery.
     
  6. guod

    guod New Member

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    just did. I was getting perfect voltage
     
  7. uart

    uart Senior Member

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    Ok I see. Well I don't much about those particular tires, but even comparing different LRR tires I've seen tests with about 8% difference in MPG. So who really knows how many percent you'll be off due to the tires, maybe 10% maybe more, honestly I don't know. But if you factor in a little extra loss due to the newness of the tires (they usually seem to take a while to break in and give best efficiency) then maybe you're down 6 to 7 MPG. That would get you back up to around 45MPG which might be about right.

    All I'm saying is that with tires that are a complete unknown it makes it hard to know if there really is any other issue or not.
     
  8. uart

    uart Senior Member

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    "double check the 12v battery. "
    Be careful. If you measure it with the car switched on (ready mode) then you'll always measure about 14 volts. This has (almost) nothing to do with the battery. You have to measure it after the car has been turned off for several hours, either with the car fully off (or in Accessory mode) to get a no load voltage and then again with the headlights on to get a loaded voltage. Ideally you want no load voltages around 12.3 or greater and headlight on voltages around 12.0 or greater.
     
  9. guod

    guod New Member

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    i followed this guide. And i have not driven the car today.

    - Without brake pedal, press the Power button once and release to enter ACC mode
    - Press and hold the MFD Info button, then turn the headlights on and off three times to enter Maintenance mode; release Info button
    - Press “Menu” (on screen)
    - Press “Display Check”
    - Press “Vehicle Signal Check” - the battery voltage is shown and should be about 12.4 to 12.8 Volts (normal for an unloaded battery)
    - Again without brake pedal, press Power button and release to put a current load on the battery - the voltage should stay above 12.0V (if less than 12.0V the battery is not well, or there is a fault or unusual load somewhere)
    - Press brake pedal and press Power button once to enter "Ready" mode - the battery is now charging at about 14V (if less than 13.6V or more than 14.4 there may be a problem with the charging circuit)
    - Turn car OFF to leave Maintenance mode
     
  10. uart

    uart Senior Member

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    Good, that's ideal. So we can rule out any involvement of the 12V battery then.

    Just out of interest what voltages did you measure?
     
  11. guod

    guod New Member

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    to get into acc voltage was 12.4, then when i pushed the power button again I got 12.1 then in ready it was 14.4 or 14.5
     
  12. uart

    uart Senior Member

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    Ok thanks. Unlikely to be a problem with the 12V then.

    You could try running a tank with bottle of fuel injector treatment though it and see if that helps. Again this is controversial as many people say those things are snake oil, but I've heard a couple of reports of it helping out, and you don't have much to lose. I'd choose any respected band name injector cleaner and take a punt. Maybe someone here can offer a suggestion. The one I heard the +ive feedback for was redline SI-1, though I have to admit I've never used (or even seen) that one myself.
     
  13. guod

    guod New Member

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    hmm. i will do some research on the cleaners and see what i come up with.
     
  14. dicklund2

    dicklund2 Junior Member

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    Cleaners work fine on my Volvo, but I always notice when it is time to get it, motor runs bad, idle gets uneven. Since we got 5-10% ethanol in all gas in sweden, I have less need for it. But it is possible that mpg will suffer before engine runs rough...

    How about engine oil, 0w/30, middle of stick ?

    Good luck!
     
  15. guod

    guod New Member

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    oil seems good as it was just changed and is at the correct level. i put a bottle of the cleaner into this tank so we shall see what happens as it goes through the system
     
  16. NinnJinn

    NinnJinn Member

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    FYI, on a prius, If the oil dip stick reads full, then it is OVER FILLED. You will want it below the full mark.
     
  17. guod

    guod New Member

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    ill check the level in a few. if it is too high, what is the best way to get it to the correct level? drain and hope for the best?
     
  18. guod

    guod New Member

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    so my oil was below the full mark so that is fine. could it be my 12v even though it has the right voltage? could it just be the age? Or is there something wrong with my HV battery? I notice that sometimes at stoplights or something if I have green (all balls full) on my MFD the engine will start revving all by itself. I read that it could be just trying to get rid of excess charge, but is that right?
     
  19. NortTexSalv04Prius

    NortTexSalv04Prius Active Member

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    Did you isolate your mileage MPG issue?
    I am starting get unfavorable mileage too
    I have done most of the suggested mpg checks
    My concern is could my O2 oxygen sensors be going out. The ICE runtime is long on pulse and glide...from dead stop ICE comes on under 28mph.
    MFD mpg is off compared to SG2 mpg in real time and avg
     
  20. guod

    guod New Member

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    i have not figured this out yet..
     
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