Gen2 Gas Mileage Mystery - Better going over Hill than on Flat !?!

Discussion in 'Gen 2 Prius Fuel Economy' started by DashingDave, Feb 13, 2026 at 3:02 PM.

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  1. DashingDave

    DashingDave Junior Member

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    From time to time I drive a Gen2 over Pacheco Pass in California (about 1300 foot / 400 meter rise).

    Puzzlingly (but not at all unwelcome) I consistently get better mileage reported (onscreen)
    for the total Up and down (~54-55mpg) - than in the subsequent miles driven over the flat Central Valley toward Yosemite (roughly 51-52mpg).

    Yes, I know I'm going varying speeds heading up and down.
    On the looong downhill section I do get up to freeway speeds (~65-70),
    versus maybe 40-ish going up the steep portion.

    Pacheco Pass - Wikipedia

    Any evidence based clues on what unusual engineering is going on here?
     
    #1 DashingDave, Feb 13, 2026 at 3:02 PM
    Last edited: Feb 13, 2026 at 3:08 PM
  2. Dany Dan

    Dany Dan Junior Member

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    We're not in the generation 5 section by chance...
     
    #2 Dany Dan, Feb 13, 2026 at 3:27 PM
  3. Trollbait

    Trollbait It's a D&D thing

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    Climbing the hill requires a higher load on the engine. For a gasoline powered one, that means a wider open throttle. More gas burned, but pumping losses are reduced, so that fuel is burned more efficiently. Then there is the coast down the other side. Even if the engine isn't shut down, little fuel is supplied to it then.

    This is why pulse and coast can improve fuel economy in any car.
     
    #3 Trollbait, Feb 13, 2026 at 4:39 PM
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