My car seems to drop to a lower gear?

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by crash0099, Dec 29, 2012.

  1. crash0099

    crash0099 Junior Member

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    When I am driving on the road between 55 MPH and 65 MPH I will be getting around 60 to 65MPG. All of a sudden the car feels like it drops to a lower gear and my milage drops down to around 52MPG. Does anyone know why this happens? The motor should be warm enough and the battery is fully charged. The Toyota shop will not even check it out if they can't duplicate it. It happens a lot. I have no clue as to why. I have a 2011 Prius III with 31,000 miles on it. It does it no matter what the temp is outside. It kind of reminds me of when your driving a lot on the battery and the motor kicks on. That doesn't happen at the speeds I mentioned does it? I am driving at a steady speed when it happens so it is not from a fluctuation of speed and the motor is not cold. I would appreciate any help for this Issue. Thanks you guys.
     
    #1 crash0099, Dec 29, 2012
  2. kithmo

    kithmo Couch Potato

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    To maintain a constant speed you would have to vary the gas pedal input according to the road conditions and the ICE will cut in/out or increase/decrease revs according to whether you are slightly accelerating or decelerating. At a constant speed then the ICE will cut in/out or increase/decrease revs according to the load, e.g whether you are going up or down a slight incline, whether there is a headwind etc.
    I would guess it happens more at say 65 mph constant speed than at 55 mph as there is more drag on the car at higher speeds.
     
    #2 kithmo, Dec 29, 2012
  3. bisco

    bisco cookie crumbler

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    it would be interesting to have an inclinometer in the car. many times, your brain tells you the road is flat, when it is actually a combination of slightly uphill, flat and slightly downhill.
     
    #3 bisco, Dec 29, 2012
    GrumpyCabbie likes this.
  4. F8L

    F8L Protecting Habitat & AG Lands

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    How many miles have you driven when this occurs? Is it happen consistently and around the same place during your commute?

    During the warm up sequence the car will go through a diagnostic function check right about the time the water temp hits 188F-191F. At this time, the car does feel like it downshifts and your instant mpg will drop 10mpg+ for about 10-15 seconds after which point it returns to the higher mpg you were getting before the check was engaged.

    I noticed this after a couple months of owning my 2012. I started watching the water temp closely and noticed it always happened right before the car reached optimum operating temp. It usually took about 5 miles or so for this to happen when ambient temps were in the high 50s.

    I did some research and my suspicion was confirmed in the tech section by Ken from Japan and others.
     
    #4 F8L, Dec 29, 2012
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