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2008 vs 2009 question

Discussion in 'Gen 2 Prius Fuel Economy' started by naid, Oct 6, 2010.

  1. naid

    naid Junior Member

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    My wife has a 2008 Prius and I have a 2009. Both were purchased within the last month. When I drive her car, I consistently get better MPG than driving mine. Wondering what the reason may be, please see below:

    2008 Package #6, 24k miles (wife's)
    Stock tires at 37 front, 35 rear
    Fresh oil change
    53 MPG average with A/C on, slightly higher with A/C off

    2009 Package #5, 32k miles (mine)
    Stock tires at 39 front, 37 rear
    Fresh oil change
    48 MPG average with A/C off


    I know about the usual suspects: bad gas, overfilled oil, etc. Will keep an eye on those as time progresses (bought my car less than a week ago, still on first gas tank).

    The reason for this thread is that the 2008 seems to use its electric motor a lot more. When doing low-speed driving, it would run on electric-only a lot of the time, sometimes discharging the battery to less than 50%.

    The 2009, on the other hand, rarely runs on electric only, even when cruising at 20-30 mph on local city streets. The gasoline engine is running a lot more than in the 2008. Also, it doesn't seem to let the battery discharge much... even when the battery is at 80%, it keeps getting charged by the gasoline engine.

    Any idea why my 2009 might be behaving this way? Or the 2008 for that matter? Not sure at this point which behavior is normal, since both cars are new to us.
     
    #1 naid, Oct 6, 2010
  2. MJFrog

    MJFrog Active Member

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    Even though it's fairly new, you might want to check the 12v battery. If the prior owner let it discharge completely (left light on or something) it could have gone bad. This would result in the ICE running excessively to try to charge it.

    You might also want to check the engine air filter. If the car was driven under dusty conditions it could be dirty.

    You said the tires were stock...were they just replaced (unlikely in an '09, but possible)? I just got new tires and my mpg has taken a 3-5 mpg hit. Should recover over the next 3-5000 miles.

    Also - YMMV.
     
    #2 MJFrog, Oct 6, 2010
  3. uart

    uart Senior Member

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    Do they have the same tire size/brand on both cars, or are they different.
     
    #3 uart, Oct 6, 2010
  4. naid

    naid Junior Member

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    Thanks for the suggestions.

    Both cars have the same tires -- OEM GoodYear Integrity.

    However, it doesn't look like the tires were rotated on my wife's car. Front tires are at 50-60% tread, the rear ones look brand new.

    On my car, it's the other way around. Front at 100%, rear at 50-60%. They were probably rotated recently which would explain a slight difference in MPG.
     
    #4 naid, Oct 6, 2010
  5. naid

    naid Junior Member

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    I did a little test tonight to figure out if it's all in my head. Drove the same loop of around 35 miles, with 80% highway and 20% city, back to back, using the same exact driving style.

    Wife's Prius = 57.9 MPG indicated
    My Prius = 53.8 MPG indicated

    I will be checking the obvious things in the next few days. Will report with results if anything definite comes up.
     
    #5 naid, Oct 7, 2010
  6. uart

    uart Senior Member

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    I only just notice that you've only owned them for a month or less. Mine took a while to adjust to my driving style and then the displayed MPG actually got better. It may get better in time, but meanwhile try checking the actual consumption at the gas pump.

    Re the engine running more often on the 2009. The gen-2 prius has some pretty strange behaviour regarding exactly when it will and when it wont cut the engine. Do a search on the "4 stages of hybrid operation" and learn about the elusive “stage 4”, this might help explain some things. :)
     
    #6 uart, Oct 7, 2010
  7. naid

    naid Junior Member

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    Problem solved!

    So the other day, I re-checked everything: tires, oil, engine air filters. All was well. Checked the cabin air filters while I was at it, no problems there either.

    I also did a battery test on both cars -- once via the "Display" menu on the MFD (hidden buttons) and once with a volt meter. Results were consistent:

    2008 Prius = 12.6V with engine off and no load
    2009 Prius = 12.1V with engine off and no load


    So I chalked up the 4 MPG difference to different voltage in the batteries, as well as the fact that the 2009 has new front tires.

    ...until I unplugged the battery of the 2009 for 15+ minutes, as someone wise suggested :D

    The mileage of the 2009 shot straight into the 60s, then stabilized in the high 50s over the next day or so. I guess the car needed to learn my driving habits from scratch.

    With some more reading and applying the MPG = 1/2 MPH to 1.2 MPH technique, the average fuel economy in the 2009 since the last fill-up (~138 miles) has been 65.5 MPG. Needless to say, I'm a happy camper :peace:

    Thanks everyone for the helpful information!
     
    #7 naid, Oct 11, 2010
  8. dabize

    dabize New Member

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    This place is great for learning to maximize MPG, isn't it?

    The "1/2 MPH to 1.2 MPH technique" - I assume you're referring to the guide for "pulse" intensity - MPG should range from 1/2 the MPH to 1.2 times the MPH - suggested by Hobbit (if I recall correctly) as a guide to the Scangauge-less unwashed (like me).

    It sure seems to help me - I've kept above 60 mpg since April using that rule......

    Recently I started using Neutral (as suggested in a thread here) for going down long hills to avoid spinning my MG1 at 41+ MPH......too soon to tell if that helps, but it seems to so far. Also helps me "hypermile" without bugging other drivers too much, since it allows me to drive faster.

    When my 12 volt goes kablooey, I'll know what to do...........
     
    #8 dabize, Oct 11, 2010
  9. Cheddaryodas

    Cheddaryodas Junior Member

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    Re: Problem solved!

    I am looking at a 2009 today, with about the same miles. When you say you ..." unplugged the battery" what do you mean? The 12V, or...?



     
    #9 Cheddaryodas, Oct 12, 2010
  10. naid

    naid Junior Member

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    Yes, the 12V.

    I did it by opening the fuse block panel and removing the cable from the red jumpstart connector.

    You can also do it by opening the trunk and disconnecting the negative terminal of the battery from the chassis of the car.
     
    #10 naid, Oct 12, 2010
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