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Significant Drop In Gas Mileage

Discussion in 'Gen II Prius Care, Maintenance and Troubleshooting' started by popptj, Jan 19, 2008.

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  1. popptj

    popptj New Member

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    I have an 07 Prius PKG 5 with 30K. The car has performed great up until now. Over the past week or two gas mileage has dropped into the 30's at times--38-40. I have not changed anything. Oil levels are fine, tire pressures are fine, etc. I notice that the battery stays green quite a bit...I read somewhere seeing a green battery is rare. I live in south Texas and it is cooler..but it's not crazy cold. Temperature has been in the 50's.

    Something isn't right. The electric/gas motor isn't coordinating as it should. To the dealership?? I can cruise at 60 and the meter is hanging in the 40's. Every now and then it will register higher mileage...say going down a hill or decline, but on level roads, nothing like before. Help appreciated.
  2. Tideland Prius

    Tideland Prius Moderator of the North Staff Member

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    how long have you had the car? i.e. have you driven it through the cooler "winter" months?

    cause at 50°F, the engine will run more often.
  3. DaveinOlyWA

    DaveinOlyWA 3rd Time was Solariffic!!

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    hard to answer without location posted... many areas of the country recently went thru much cold than normal weather. are you in one of those areas?
  4. popptj

    popptj New Member

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    Temperature is 60 degrees currently and still having the same problem. I am convinced something is wrong mechanically. I have heard about "flashing" the system at the dealer. Any thoughts on that or other potential fixes?

    I have driven it in similar weather before here with good results a month ago or so.
  5. DaveinOlyWA

    DaveinOlyWA 3rd Time was Solariffic!!

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    60º.... ya, even if you drove like a maniac, you probably couldnt do worse than 40 mpg as long as you kept it under 70... i would have it checked along with tire pressures.

    my mileage took a dive once, more than 5 mpg... found out that had a tire down to 21 psi from 40... will say one good thing about LRR tires, they keep their shape well even with little air pressure
  6. uncool

    uncool New Member

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    Im in the bitter cold of Chicago where my high 40s mpg are currently low 30s.
  7. AOV

    AOV New Member

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    Winter and the heater is ruining my mpg's. Use to get mid to high 50's on a regular basis during the milder weather, now that it is 20's and 30'sF here, and with numerous short trips (less than 15 min. round trip) my mpg's are low 40's. Just came back from a 500 mile round-trip (highway mostly) and only got 45, used to get a lot more. I keep the cabin air at about 73 degrees.
  8. gazz

    gazz Member

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    Its colder in the UK and I have dropped from 65s to 55s. Does not matter what I do it just will not get the summer mpg. Tried all the trick (block heater. tires, running with heater off) I think it is just a fact you will drop 15%.
    What I am doing is taking some readings on different points of my trip to work so I can compare them in the summer, and try to understand when the loss occurs.

    The warm days will be back soon :)
  9. ml194152

    ml194152 New Member

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    My wife had a major front-end wreck with her Prius ($10K damage) and when we got it back, it was suddenly averaging only 35 MPG, whereas before she always got 45MPG (Houston, TX, summertime). We took it to the dealer and had them check about the gas mileage. They said they hooked up a meter to it and drove it 20 miles down the freeway and back and they said it was getting 37MPG which to them was "normal". So nothing was done. One month later I checked her mileage and it was at 45MPG.

    I think you should just wait until summertime and see if it corrects itself. Winter is a killer for gas mileage, as everyone here will tell you. Even 60 degrees will reduce MPG from when temps are in the 90's.
  10. GreatOutdoors

    GreatOutdoors New Member

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    I have the same problem -- starting in January my gas mileage inexplicably dropped from about 45 to about 38. No explanation. And I live in Southern California, so please no one tell me it has something to do with the cold weather! I got new tires last September and I had a 35K check-up in December. My unhelpful Toyota mechanic said that if something was wrong there would be an engine light on (which there isn't). So I guess nothing's wrong? I want my old gas mileage back!
  11. BAllanJ

    BAllanJ Active Member

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    Winter gas? Slightly dirty MAF sensor? How's your 12 v battery?

    Mine just climbed back to 4.7 l/100km (~50 mpg) with warming weather and switch back from winter tires... I got 5.7 l/100km over the winter.
  12. gwendt

    gwendt New Member

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    I just had a significant drop in gas mileage - my second. I normally get 49 - 50 in SF Bay area. After changing the oil 2 days ago I noticed the mileage dropped to 30 - 40. WOW! This happened once before and finally corrected itself after several weeks.
    The one thing I do notice is that when I accelerate now the average mpg bar goes way down to 10. It usually sticks around 25. I have no explanation for this. I thought that due to servicing the MAF sensor might be disrupted or something but after cleaning the behavior didn't change.
    Also the engine/electric motor seems to be acting differently. I previously asked the Toyota Tech about this and they checked it and said everything is normal - Whose normal? Theirs or mine?
    Anyway if anyone comes up with a reason for sudden drop in gas mileage I am all ears.
  13. Genoz World

    Genoz World ZEN-style living

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    OK, it's been said before, but I would start with these suggestions.

    #1) Make sure that they put the correct viscosity in your car. your gen II takes 5/30W. They might have put 10/30 or higher. (hopefully not)

    #2) They might have OVERFILLED it. Take your dipstick and check the oil level. I place no more than 3.75 quarts in, and that's it. any access can hinder gas mileage.

    #3) Check your tire pressure. Make sure that you have 42/40 or 40/38 psi in the tires, the higher psi in the front. Sometimes the dealer will DROP the psi to normal specs.

    #4) Check your air filter.

    #6) Drop in a bottle of CHEVRON fuel injection cleaner.

    Anyone else for suggestions?
  14. gwendt

    gwendt New Member

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    Thanks for the input:
    1) I specifically request the 5/30. (Castrol if I can get it)
    2) Oil level is perfect.
    3) Specifically ask that 4 PSI is added to Toyota recommended. (40/39)
    4) Clean - so is the MAF now.
    5) Odd that the fuel injectors would act up exactly after an oil change. Anyway, added fuel injector cleaner the last time this happened to no avail.

    Something changes during the engine inspection and what they do while working on the car. Just can't figure out what it is.
  15. richard schumacher

    richard schumacher shortbus driver

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    One of their drivers or techs leaves the car ON for a few hours and burns off some fuel. Presto, lousy MPGs until you drive it for a while and fill it up.

    Uhh, "engine inspection"? What are they doing, exactly? That's not on the list of items in the Scheduled Maintenance Guide.
  16. cycledrum

    cycledrum PSOCSOASP

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    Is there any draginess in your parking brake?

    After my 2nd service, the parking brake felt very stiff - it would engage almost immediately when pushing pedal down. Also, in D, foot off accelerator, car would barely creep forward ....

    culprit - parking brake overtightened, rubbing on rear drums. This was fixed immediately.

    Anything like that happening with yours?
  17. gwendt

    gwendt New Member

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    Good question. I had a problem with the parking brake about a month ago. Had to have the car towed to Toyota it was dragging so much. They replaced the cable, and adjusted the emergency brake. I don't set the brake that often maybe they did while servicing. I'll check it tonight when I leave for home.
  18. mark010101

    mark010101 Junior Member

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    Another factor in the equation is the difference between the winter and summer blends of gasoline.
  19. Shin Chan

    Shin Chan Junior Member

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    I noticed a 3-5MPG drop in mileage just before the 12v battery died. I replaced it and within a tank of gas I was back up into the 48.4MPG were I normaly am at.

    Just my two cents
  20. richard schumacher

    richard schumacher shortbus driver

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    BTW you really should use the parking brake every time you park. Using it keeps it from rusting up.
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