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  1. #1
    Junior Member
    Join Date
    Oct 2008

    Gas Mileage Drops 15% after Maintenance

    I have kept meticulous records of my driving habits and mileage over the first 40,000 miles with my Prius. Result: 54.4 mpg. Then I took my the car into the dealer for its 40,000 mile maintenance: new tires, cleaned the intake manifold, alignment, adjust brakes, change oil, replace filters. Now my car is getting about 46 mpg. A drop of over 15%.

    I had Toyota recheck everything they did. They say there is no problem. I am pretty sure the tires are the same type that came with the car: Goodyear Integrity. I am using the same tire pressure: 42 psi front, 40 psi rear. I specifically asked about the brake clearance. They said it was fine. They "recalibrated the fuel trim". Still no change. The alignment feels good. My driving patterns have not changed.

    I am really at a loss as to what to check.

    I know that many people only get 46 mpg with their Prius and I'm sure that is why Toyota is not really concerned. It is frustrating because I know what the car can do and has done for the last 40,000 miles.

    Of course, this may have nothing to do with the maintenance work: it could be a coincidence.

    Any suggestions?

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  3. #2
    Junior Member
    Join Date
    Dec 2007

    Just a thought, but the

    Just a thought, but the car's memory may have been reset.

    The car keeps track of your driving habbits, and tries to optimise it's performance to your driving style, road conditions, etc.

    I normally drive short trips around the city and suburbs.

    When I take a long road trip, 1,000 miles on the expressway, I find that for the first 200 miles or so, the car gets lower mileage. Then after a few hundred miles on the expressway, the mileage rises about 5mpg.

    THEN, after the long road trip, back on city driving, I get 5-7 miles less mileage for a couple hundred miles, then the mileage creeps back up to normal for city driving.

    Your car may just need a few weeks to build up it's memory of your driving habbits and road conditions.

  4. #3

    I have the same exact

    I have the same exact problem. I took my car in for 45000 mile service, plus new tires and my mileage tanked afterward. I was getting 51-53 mpg. Now I'm lucky if I get over 45.

    And in New England the cold weather has hit hard - this last tank I'm under 40.

    No idea what's going on.

  5. #4
    Junior Member
    Join Date
    Dec 2007

    May be just coincidental

    May be just coincidental with cold weather arrival.

    Question: how much of your driving is "short trips" like under 10 miles.

    It is a fact of life that EVERY gasoline powered engine uses almost twice as much fuel when it is cold. That is why every gas engine has a choke. From chain saw, to motor home.

    That means for the first 1/4 mile in summer, or for the first 2 miles in the dead of winter, your Prius is getting only half it's normal mileage. You should see this on the 30 minute mileage display.

    Short trips in winter, mean lower mileage because the engine is running cold for a major portion of the trip.

    The only good news, is that the Hummers have the same problem. A 4mpg Hummer only gets 2mpg when it is cold.

    The big difference is that the Prius gives us several types of mileage read-out, so we are more aware of the mileage loss.

    AND... if your computer's memory was erased, do not dispare, the car will reprogram itself to your driving habbits, and improve it's mileage within about 300 miles or so.

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