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Another reducing mileage post: actually going down minute by minute

Discussion in 'Gen 2 Prius Fuel Economy' started by piratesbooty, Jun 20, 2011.

  1. piratesbooty

    piratesbooty Junior Member

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    Hi all,

    Long time Prius owner (been about 10 years and this is my 2nd one, Gen II). I have a 2006 and have consistently gotten 46 miles per a gallon. My car has about 50k miles on it. Rain, snow, cold weather, hot weather, didn't matter, very little fluctuation. About 6-8 months ago, my mileage dropped to about 41. I thought it could be winter but it didn't matter what the temp was--still 41.

    I changed the tires and no improvement. Last week or two ago, I changed my cabin air filter myself and looked at the engine filter (which was recommended to me by a fellow Prius owner). Since then, my mileage has dropped into the 30s. I'm at about 39.5 and I can actually watch it drop as I am driving. It's making me crazy. I am bringing the car in on Thursday but wanted to see if anybody had any thoughts or has had luck with the dealership with these issues. Thanks!
     
    #1 piratesbooty, Jun 20, 2011
  2. cwerdna

    cwerdna Senior Member

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    #2 cwerdna, Jun 20, 2011
  3. qbee42

    qbee42 My other car is a boat

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    What sort of SOC behavior have you witnessed? Are you still using the original 12V battery?

    Tom
     
    #3 qbee42, Jun 20, 2011
  4. ystasino

    ystasino Active Member

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    If you reset your MFD mpg and drive your car on the highway for 20 minutes at 50 mph with cruise control what's your mpg for that trip? Note that A/C usage has minimal impact at these speeds.

    If you drive your car on the highway for 20 minutes at 50 mph and then come to a complete stop does your engine stop withing 5-7 seconds? Note that A/C must be turned off before you come to a complete stop for this test.

    Dealers usually don't do anything unless there are codes or warning lights. My suggestion is to establish whether your traction battery is going bad, before you go to the dealer. If you document that the traction battery is faulty you must go and register your complaint so that there will be a record with the dealer and also call Toyota customer experience.

    In essence you will be documenting that your traction battery is failing so even if it fails after the 8 year warranty expires you will have evidence that the problem occurred prior to the warranty expiration deadline.

    Answering questions about changes in your route, A/C usage, state of charge (SOC) status during normal operation (does it drop to 5 or 4 bars ever?) and 12 V battery condition is necessary.
     
    #4 ystasino, Jun 20, 2011
  5. piratesbooty

    piratesbooty Junior Member

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    - Have you read Yet?

    I just read this article.

    - What fuel economy are you getting and how are you determining fuel economy? (trip computer or manual calculations)

    I am now getting 39.5 mpg, down from 46 mpg, for a 4- year period. I use the trip computer. There is NO change in route, driving techniques...same everything.

    - What fuel economy are you expecting and why?

    I am expecting the 46 mpg because it has been very consistent over the last 5 years.

    - What are the approximate outside air temps?

    It doesn't matter for this particular issue. It dropped to 41 mpg about 6-8 months ago with no change according to temperature.

    - How long are your trips?

    I am judging this by overall. As I said, my routine has not changed.

    - 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?

    See above.

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

    Not that it matters, but MD. And the car has primarily been driven in MD.

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

    Flat.

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

    Not unless the dealership has overfilled it.

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


    It is the original car battery. Is 5-years the witching time for these? I am not sure what my voltage over night is.

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

    Yes and no.

    - 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).

    Tires were replaced about 5 months ago. M+S P185/65R. A very small decrease in mileage.

    - What are your tire pressures?

    I'm not sure...but this have something to do with it.

    - 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.)

    Not sure. I had a first gen Prius. Mileage fluctuated with temps (lived in VT and MA).

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

    I drive "regularly". Not a lead foot, nor trying to stay on electric.

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

    No.

    - Are you driving using D or B mode?

    No.

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

    Again, doesn't matter. Total decrease regardless of heater/AC.

    - If reporting a mileage drop, did anything significant change on your car (e.g. accident, hit a curb or big pothole throwing off alignment, oil change/other maintenance/repairs, changed tires or wheels, etc.) or your commute?

    No.

    I have an appointment to take it in on Thursday. I did try and change the cabin filter myself and the engine filter (but didn't actually change the engine one). Things have gotten worse since then. I did bring it in for a diagnostic 4 months ago after the tire change and they could find nothing wrong with it.
     
    #5 piratesbooty, Jun 21, 2011
    1 person likes this.
  6. uart

    uart Senior Member

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    You need to give the exact brand and model of your tires and also their inflation pressure. Its important, tires are one of the most common reasons for lost MPG.

    BTW. Cabin filter wont really have any effect on fuel economy.

    How dirty did the (engine) air filter look?
     
    #6 uart, Jun 21, 2011
  7. piratesbooty

    piratesbooty Junior Member

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    They are Goodyear M+S P185/65R. I guess I need to get the PSI. Should they be filled to 40?

    The engine filter did not look dirty...it appeared to have been changed recently.
     
    #7 piratesbooty, Jun 21, 2011
  8. piratesbooty

    piratesbooty Junior Member

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    The model is Integrity.
     
    #8 piratesbooty, Jun 21, 2011
  9. seilerts

    seilerts Battery Curmudgeon

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    You have way too much faith in your dealer. 99% of the time, if you ask them to diagnose a car when the check engine light is not on, they will find nothing wrong. Owning a Prius requires a "trust but verify" sort of mentality. If they change your oil, pull the dipstick and make sure that it is at the proper level. Check your tire pressure. Check your 12V, it is the most common source of unexplained poor fuel economy, see http://priuschat.com/forums/newbie-forum/73400-weird-stuff-happening-mpgs-dropping-test-battery.html. The reason that a bad 12V battery will cause poor fuel economy is that the charging system, which runs off the high voltage system, is trying fruitlessly to charge the 12V, and instead the energy is wasted.
     
    #9 seilerts, Jun 21, 2011
  10. nerfer

    nerfer A young senior member

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    Yep, might be time to change the battery. Probably better to do before it goes really bad on you, 5 years is about their lifespan.

    But also check those tires. The recommendation is 35 front 33 back, but a lot of people put a little extra air to improve tire life and mileage. I keep it about 39 front and 37 rear (10% high, which is well within the rating of the tire itself). The dealership sometimes lowers the tire pressure on new tires or selling new cars because it gives a softer ride, but it reduces the tire life, reduces your mpgs, and too low of pressure can be dangerous as it leads to blowouts.

    If it's not these two things, then there might be a slight fuel leak someplace or something more complicated. Have you noticed a gas smell in your garage? (Assuming you keep it garaged). Watching the mpg is how I first detected a fuel leak in my VW bug.
     
    #10 nerfer, Jun 21, 2011
  11. ystasino

    ystasino Active Member

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    Definitely time to change the 12 V battery, but in my mind it is unlikely to be the answer to your efficiency drop.

    Does your HV battery ever drop to four blue bars? can you drive the car using the yellow arrows only or does the ICE work much more than it used to thus keeping your battery to six and seven bars?
     
    #11 ystasino, Jun 21, 2011
  12. cwerdna

    cwerdna Senior Member

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    Agreed that it is about time to change the 12 volt battery (I did on my 06 a few months ago). However, changing it may not solve your apparent mileage drop.

    Concur w/check your oil level and tire pressures along w/inflating above 35 front, 33 back.
     
    #12 cwerdna, Jun 21, 2011
  13. Mendel Leisk

    Mendel Leisk EGR Fanatic

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    There's more to the name: Goodyear's the brand, M+S is the traction rating (any all season tire will say M+S), but there is some model name, ie: they're Goodyear Assurance, Elantra, or something. Goodyear FuelMax would be a good one.

    For sure check pressures. 40 sounds good, maybe a little less for the rears, say 38.
     
    #13 Mendel Leisk, Jun 21, 2011
  14. Muhahahahaz

    Muhahahahaz Member

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    He said Goodyear Integrity in the very next post.
     
    #14 Muhahahahaz, Jun 22, 2011
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