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I'm not sure what's going on with mileage

Discussion in 'Gen 2 Prius Fuel Economy' started by m.waff2, Dec 4, 2017.

  1. m.waff2

    m.waff2 New Member

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    Oregon, U.S
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    2004 Prius
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    N/A
    So, I purchased my 2004 prius a while ago (mostly in a bind). I love it, but now that I've hit 155k miles I'm noticing my gas mileage dropped A TON! I went from avg of 55 mpg down to now about 35-38. It seems to be cycling more rapidly. I was at a drive thru today and it kept kicking on and then off, just to turn back on. It is cold here, so my heat was on, and I was in the drive thru 8 minutes. It's just irritating because I'm definitely out of warranty and I'm concerned this could be the hybrid battery? I just got new tires, just did a tune up, and am about 5k from an oil change. I simply have no way to manage the cost if it is the hybrid battery since I'm in school still and that's most of my money right there.

    Is there anything else it could possibly be? I live in a wet, cold state so I know that will impact my mileage but last winter even in snow I was still averaging higher than this. Any help is appreciated. Thanks!!
     
  2. fotomoto

    fotomoto Senior Member

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    Rapid cycling of the battery SOC (state of charge) and decreased MPG's are two signs that can point to a weak hybrid battery. If it's still the original HV battery, plan accordingly regardless.

    New, non-LRR tires can cause a dramatic drop in MPG's too. What kind does it have?

    Using heat especially over short distances will cause the cold gas engine to run a LOT more which drops MPG's too.

    Thicker oil can lower mpg's also.

    GOOD LUCK!
     
    SFO, valde3 and Raytheeagle like this.
  3. Kevin_Denver

    Kevin_Denver Active Member

    Joined:
    Mar 18, 2016
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    Location:
    Denver, CO
    Vehicle:
    2009 Prius
    Model:
    N/A
    First thing to check is your 12V battery. A low 12V battery will make the inverter pull extra current from the HV battery, draining it more quickly and costing mpgs. Many posts around here on this.

    New tires, especially ones with a lot more rolling resistance will reduce mpg. What tires you have on it versus previously? Also note that new tires usually suffer from worse fuel economy for ~500 miles as they break in. See where your're at after two tanks.

    Also, what was involved in the tune-up? A good practice after changing items like the spark plugs is to disconnect and reconnect the battery to reset the ECU to let it remap to changes in the engine.

    The Prius engine gets heat starved quickly and will turn on the engine a lot in cold weather with the heat on when stopped. I personally set the heat to 65 degrees with the fan on the lowest setting and bundle up when driving around town in the winter to help keep the engine warm. Even with 75% of my grill blocked the temp will drop fast when it's below freezing out when the car is stopped. On the freeway it's no problem though - water temp reported on my scanguage quickly rises to 85C and stays there - then I turn up the heat. If you haven't yet, look into partially blocking the grill in the winter time.

    To me it sounds like a combination of ECU resetting itself, new tire break in, cold weather, and going through a drive through with the heat up that's affecting your fuel economy.
     
    SFO likes this.
  4. 05PreeUs

    05PreeUs Senior Member

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    Based on your description and the current climatological conditions, I would say that the thermostat is not allowing the engine to get up to operating temperature causing excessive on-off cycling of the engine and the subsequent decrease in FE.
     
  5. bisco

    bisco cookie crumbler

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    it's probably a clogged air filter, no worries, very common in the 2004, especially in oregon. remove it, tap it on the ground a few times, replace, and you're good to go.
    all the best!(y)
     
  6. tai_prius05

    tai_prius05 Junior Member

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    Vehicle:
    2019 Prius
    Model:
    LE AWD-e
    Bisco
    I’m impressed, I have seen your posts in a few threads and you seem spot on. Thanks for great advice. I will be using your recommendations for my few issues. (Gas gauge and mileage)

    Will let u know outcome. Question. I joined this when I purchased my car in 2015. There used to be mileage threads (100k, 200k, etc). Are any long mileage threads still going? Could not find. My car is 215k+. And would like to hear about other experiences from travelled friends.

    Thx. Tai
     
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  7. bisco

    bisco cookie crumbler

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    yes, the threads are still here, but search is sometimes difficult. there are all pinned in the gen 2 main forum.
    congrats on your 215k, keep her going!(y)