Dispiriting drop in mpg, then breakthrough

Discussion in 'Gen 2 Prius Fuel Economy' started by ksspyder, May 22, 2013.

  1. ksspyder

    ksspyder Junior Member

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    Saw a drop in mpg from 45mpg to 34mpg. Since I was way over 200,000 miles, I began to fear traction battery failure. Toyota looked over codes, did diagnostics, etc. and found nothing. They recommended and replaced auxiliary battery, which made no difference. I fought with them on aux. battery replacement price since their costs had gone up 50% in two years. Mine was barely out of warrantee.
    So what happened. I replaced the iridium plugs. Mileage jumped back up to 45mpg.
     
  2. Mendel Leisk

    Mendel Leisk Sand Pounder

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    First or second replacement?
     
  3. wfz

    wfz Junior Member

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    so is it the iridium plugs or the change of plugs makes the difference? Iridium plugs appear to be much more expensive and I wonder if it gets similar result with other types of plugs.
     
  4. JimboPalmer

    JimboPalmer Tsar of all the Rushers

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    No Prius uses any other type of plugs. They are all irdium as stock.
     
  5. icharry

    icharry Junior Member

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    Great news... my 60,000 mile 2007 has seen a drop from a VERY steady lifetime city/freeway combo of 45mpg down to about 35mpg over the past 6 or 7 tankfulls. The Toyota dealer said it could be so many things - like weather (I live in So Cal) or my driving style and so on... but I keep detailed records and I know something is different. Even when I just leave the gas station and pulse/glide I used to get easy 60+mpg fo the first few miles... now not so much.

    Guess I gotta check the plug - but would that have an effect even if/when I pulse/glide out of the gas station almost all downhill to my next regular stop? Any other thoughts?
     
  6. nh7o

    nh7o Off grid since 1980

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    One thing to make sure of is that your engine is actually shutting off when coasting. One of the symptoms of a bad 12V battery, which will not take a charge properly, is that it keeps the inverter running excessively and that keeps the engine running when it otherwise would shut off.
     
  7. Kengatorfan

    Kengatorfan Junior Member

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    Iridium plugs cost at most $8 each vs. $2 for regular plugs. With the increased mileage they will pay for themselves on the first tank of gas. My wife's '06 Corolla uses Iridium plugs. I replaced them when they caused a warning light on the dashboard. Saved a $60 diagnosis charge from the dealer stealer.
     
  8. usbseawolf2000

    usbseawolf2000 HSD PhD

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    The maintenance schedule called for the plugs change at 120k or 150k miles. So, 200k is a bit of a stretch. Do you still have the old plugs? I'll be interested to see the condition.

    I changed my 2006 Prius plug at 113k miles and they looked like this (left Denso is new). The gas mileage may have improved a little (0.5 or 1 MPG?) but it was barely noticeable, suggesting the plugs still had life.

    [​IMG]
     
  9. Mendel Leisk

    Mendel Leisk Sand Pounder

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    I had a look at the plugs on my 3rd gen, last weekend, and I would not wish that chore on anyone (kudos to NutzAboutBolts for his step-by-step video).

    Toyota in their wisdom has made it impossible to extract the plugs without removing wipers, bottom-of-windshield trim, wiper motor/linkage and metal cowl (c/w brace).

    The actuators have a rigid snorkel piece running down to the spark plugs in the well. With a few inches increase in clearance to cowl, or redesign of the actuator to somehow make it flexible, none of the above tear-down would be needed.

    Anyway, the plugs looked great, at a mere 36000 km's. ;)
     
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