Sudden increase and then drop in MPG

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by priusphan, Jul 14, 2025 at 5:30 PM.

  1. priusphan

    priusphan New Member

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    I was torn between posting this in the fuel economy area or here so please let me know if I should move it.

    I have a 2013 prius with 133000 miles.
    I normally get about 47 MPG (Calculating at the pump, not with the onboard computer). A couple of tanks of gas ago I suddenly got about 51 MPG. Then the next tank it suddenly dropped to 37 MPG and has remained low for the past 3 tanks.
    This seems to be mostly for city driving. It still gets 47 MPG on long trips.

    Any help on what might have caused this spike and then drop would be greatly appreciated.
     
    #1 priusphan, Jul 14, 2025 at 5:30 PM
  2. bisco

    bisco cookie crumbler

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    all recommended maintenance done? have you cleaned the egr circuit? tyre pressure at or above spec?

    might be worth checking all the wheels for brake drag, and getting a free 12 volt load test at many auto parts stores
     
    #2 bisco, Jul 14, 2025 at 9:03 PM
  3. Grit

    Grit Senior Member

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    Maybe more AC use now were in middle of
    Summer. Or late night driving with stock headlamps on. Each lamp
    Is about 55 Watts
     
    #3 Grit, Jul 14, 2025 at 11:43 PM
  4. ASRDogman

    ASRDogman Senior Member

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    Is it the same pump everytime? Or a different one?
    Pumps cut off at different time. The "should" all be the same, but they are not.

    It happens to me sometime. I try to use the same pump at the different stations I go to.
    But it's not always possible. This past few weeks the Prius said I was getting 48mpg.
    When I filled, it calculated to 51mpg.
    The next week it said 47 something, calculated, 43 something.... both times I used a different
    pump then I usually used. It happens from time to time.

    When each time you fill it it lowers, you have an issue. You should look for consistency.

     
    #4 ASRDogman, Jul 15, 2025 at 7:46 AM
  5. Mendel Leisk

    Mendel Leisk MMX GEN III

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    Bad gas?
     
    #5 Mendel Leisk, Jul 15, 2025 at 9:27 AM
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