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2007 Prius 10 MPG decrease after 90k maintenance and new tires

Discussion in 'Gen 2 Prius Fuel Economy' started by Leanne C, Jan 14, 2014.

  1. Leanne C

    Leanne C New Member

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    Hello everyone,

    I'd recently gone to a auto repair shop to get my 90k maintenance done. They don't specialize in Toyotas or Prii but the local Toyota dealer is notoriously bad so I didn't fancy going there. Anyway, I'm used to getting 42-43 MPG normally, which I know isn't stellar but is still acceptable (I think) for its age; however since it came back from the shop I've been getting 33-34 MPG, which is pretty terrible for a Prius. I also have new tires (Goodyear Assurance Fuel Max). It's reasonable to assume that since my old tires were pretty much at the legal limit, having brand-new treads should increase friction and thus lower the fuel economy by a bit - but not by 10 miles per gallon.

    I'd appreciate any insight from experts and more experienced owners.
     
  2. bisco

    bisco cookie crumbler

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    welcome to priuschat! the tyres might be good for 5 mpg until they are broken in. make sure the pressures are up around 40. what else did you have for service?
     
  3. dorunron

    dorunron Senior Member

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    What bisco said, check the air pressure. Probably set to placard. Run at least 40F 38R Also check the oil level. Too much oil can contribute to low MPG. Will take a while for the new tires to break in. Are you certain that the correct weight of oil is being used in the engine? Is it 5W30 or 0W20?

    Welcome to Prius Chat!
     
  4. JC91006

    JC91006 Senior Member

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    you spell tyres like John (britprius)
     
  5. bisco

    bisco cookie crumbler

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    i love the way it looks.:)
     
  6. tanglefoot

    tanglefoot Whee!

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    I've heard of service departments adjusting the parking brake too tight. Does it feel like the car isn't coasting as well? I agree to get some more air pressure in the tires. I use 44 psi front/40 rear but you can choose your pressure, just put 2 psi less in the rear tires than the front. Has there been a weather change? Cold weather definitely reduces MPG. I also second checking the oil level. Shops sometimes overfill Prii, since they only take 3.5 quarts.
     
  7. Leanne C

    Leanne C New Member

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    I don't know what the pressure's at right now but I will check when I leave work today. I have no idea about the oil level or weight; I'll try to find out as well.

    As for the service, here's the description from the invoice:

    "Change oil filter, inspect belts, hoses, fluid levels and condition. Inspect brakes, steering, and suspension. Rotate tires. Fixed front seat squeaking issue and replace right rear tail bulb."

    In addition I also got my coolant drained and replaced since the pH was at 11, by a gas station (the Toyota dealer wanted to charge me $475). Could this be a source of the problem?

    Thanks for the input so far!
     
  8. bisco

    bisco cookie crumbler

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    i don't think coolant would affect mpg's.
     
  9. uart

    uart Senior Member

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    He's from Boston, but he never attended the tea party. :cool:
     
  10. uart

    uart Senior Member

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    Start with the simple things.

    - Check tire pressures. You want at *least* F/R = 36/34 psi (40/38 is better for mpg).
    - Check the oil level (on the dipstick, car on level ground, engine off for 10+ min).
    - Check the coolant level. (at main radiator cap *not the plastic expansion tank*, engine off 30+ min).

    The coolant level probably wouldn't effect the MPG, but it's always a good idea to check any fluid levels after anyone else has touched them.

    If everything above checks out ok then don't panic, a lot of times these mysterious losses of mpg sort themselves out over a period of several weeks (maybe even one or two months). It appears that many mechanics disconnect the 12V battery for safety when doing even mundane work on the Prius. This removes some learned data (aka historical data) from the ECU and it takes a while to relearn. In your case you've got the second factor of new tires which might also give a small mpg hit until they're "broken in" after a few thousand miles.
     
  11. Leanne C

    Leanne C New Member

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    Hi uart,

    Checked tires today & filled them up to 40 each; the guy at the gas station said oil and coolant looked fine too. It probably is the data erasure like you said, the MPG metre does seem to be climbing slowly. Thanks for the help.
     
  12. Kishore

    Kishore Junior Member

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    I had similar issue-got an oil change and "bam"- mpg dropped from 46-47 to 39. What the :mad:- I waited for a few days and then made a call back to set up time with the shop. Next day my mpg is back to normal levels I typically see (y)

    It is as if my Prius heard the call and made amends....

    regards,
    Kishore
     
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