Possible undiscovered performance and MPG issues with Prius v (lowercase v)

Discussion in 'Prius v Fuel Economy' started by kirill626, Mar 31, 2015.

  1. Seanathon

    Seanathon Junior Member

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    Just wanted to chime in here as this page came up on my search for my 2012 Prius V is averaging 31 mpg at the moment, best ever all year being 36 mpg. This is one of the first batches of the Prius V, our family bought it the first year of its release. I can relate to the "pulling trailer" sensation, the car definitely feels like it is being pulled back, a sort of "phantom braking" if you will. I can't tell what it could be. I lifted the car to spin the wheels and front two spin freely, rear spins as freely as any other rear wheel would (parking brake just touches it so it's not like a bicycle wheel, about one revolution and it stops). I am motivated to find out what the cause for this could be, it's really a head scratcher. All tests in Torque app are green, new spark plugs, no apparent issues. It's a mystery.
     
  2. Mendel Leisk

    Mendel Leisk Cloud Watcher

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    Are you sure the fronts "spin freely"? Is this maybe with car on and in Neutral?

    The rear brakes on the Prius v are a little different than regular 3rd (or 4th) gen Prius: they have an integrated mini-drum brake, for the parking function. I don't have the repair manual for Prius v, but with a short-term Tech Info subscription you should be able to scoop the brake info. There's likely a procedure for checking proper operation of the parking brake, adjusting if needed.

    FWIW, with my 3rd gen Prius, albeit with a different parking brake system, with a good push the rear wheels will spin 2~3 revolutions.



    Maybe not that much difference?
     
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  3. rjparker

    rjparker Senior Member

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    The Prius v has a different 'drum parking brake' integrated into the disk rotors in the rear than standard gen3s. So it could be an issue.

    The typical mpg problems are a low capacity hv battery that is not storing and returning enough power to assist the gas engine. This can easily cost four mpg. A really bad 12v battery can cause an excessive charge current that can waste mpg. This is far less common as most 12v batteries just fail to hold voltage. Wheel bearings can cause a drag when worn and will not exhibit the typical looseness. They will howl at speeds around 35-50 mph until increasing road noise drowns them out. Rear hub bearings on the v are becoming more common as higher miles accumulate. Deduct another four mpg for one bad bearing.

    Extremely poor gas octane will decrease mpg while higher octane will slightly increase mpg. However Premium or ethanol free gas is not worth the increased cost. But substandard regular is not worth it. Just because a Costco gas is a low price does not mean its bad. Most gas in a given area comes from one to three refineries by pipeline with only locally injected detergent additives making the marketing difference. Sometimes the worst refiners will cheat a bit on octane.

    Driving habits are a significant factor as well. If you have a light foot on initial acceleration, anticipate stops to maximize regen, let off slightly when going downhill rather than gaining speed and stay below 65 mph most of the time, the epa mpg of 42 for a v is possible. Just yesterday I averaged 45 mpg displayed on a hundred mile trip heading north to Austin on a 65 mph freeway. Returning on a parallel 85mph tollway would easily reduce mpg to 36 for that leg. And cost $6 for tolls. Lifetime displayed mpg is 41.5 over 250k miles, some with a failing hv battery and a worn bearing.

    What you often find on these forums are satisfied users with low miles and early maintenance schedules. Others like me rolled 30k miles a year for the first eight years and experienced many issues others are just reading about. With 250k miles on the odo, mpg is something that matters to me. Its about the only reason I still have this car.
     
    #123 rjparker, Dec 4, 2021
    Last edited: Dec 4, 2021
  4. Seanathon

    Seanathon Junior Member

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    Thank you Mendel, you make a good point. I will have to double check the front wheel and exactly how freely they spin if at all, in park it certainly wouldn't spin (my memory recall isn't too great!). The rear wheels give some resistance, there is an adjuster on the rear brakes that moves the shoes closer or away from the drum. I will have to play with readjusting it, perhaps a notch or two looser, it is possible it is sitting too close to the drum at the moment.

    Thanks for the video, now this is a wonderful reference. From the sound, if I'm not mistaken, I could hear the parking brake is just lightly touching the drum. I'll have to give this a shot tomorrow and see just how many revolutions the rear wheels spin with a strong push. This could explain the "pulling a trailer" feeling I have with my car.

    It's almost 10 years on the original 12v battery, and "cold" voltage is 12.2v according to the vehicle reading, sounds like it's worth replacing anyways, and I'd consider it a blessing if it does address the mpg issue!
     
    #124 Seanathon, Dec 4, 2021
    Last edited: Dec 4, 2021
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  5. Tim Jones

    Tim Jones Senior Member

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    290,000 miles 44...45 mpg
    front tires 42
    back 38
    Michelin Defenders
     
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