1. Attachments are working again! Check out this thread for more details and to report any other bugs.

Crazy 199 MPG when going down big decline

Discussion in 'Gen 4 Prius Fuel Economy' started by robsnyder20, Feb 7, 2017.

  1. robsnyder20

    robsnyder20 Active Member

    Joined:
    Aug 13, 2012
    374
    301
    0
    Location:
    SW Florida USA
    Vehicle:
    2016 Prius
    Model:
    Three
    SP32-20170207-223234.jpg Standard Gen 4 Prius not Prime

    I came back from a trip and had a couple questions about using B and going down hills. My RPM was up high, as expected to hold speed which worked very well and on my torque app, it shows that I was getting about 50 MPG and using fuel, but somehow, my car indicated that I got 199 for the trip and instantaneous downhill. I was at the top of a peak in the smokies, called Clingsmans dome, coming thru Gatlinburg, TN into Pigeon Forge. Here is a pic of the readout. I am from Florida so not used to elevation changes, but I consider the prius suspect for not indicating MPG correctly upon B decel.

    I did reset the trip and can confirm even though the engine was near redline 4+k (thru torque app) and showing a .5 to .7 MPG fuel use and 40 - 60 MPG, my car said I am getting 199 instant.
     
    #1 robsnyder20, Feb 7, 2017
    RCO and krmcg like this.
  2. JimboPalmer

    JimboPalmer Tsar of all the Rushers

    Joined:
    Apr 14, 2009
    12,470
    6,871
    2
    Location:
    Greenwood MS USA
    Vehicle:
    2012 Prius v wagon
    Model:
    Three
    I do not own a Gen 4 and this is just speculation.

    There are two different ways to measure MPG in this scenario.

    One would be to only consider gas used times miles driven.

    The other would add the charge stored that will later become free energy.
     
    #2 JimboPalmer, Feb 8, 2017
    RCO likes this.
  3. robsnyder20

    robsnyder20 Active Member

    Joined:
    Aug 13, 2012
    374
    301
    0
    Location:
    SW Florida USA
    Vehicle:
    2016 Prius
    Model:
    Three
    For whats its worth, the opposite way going up I got 21 MPG the steepest area of the climb (which was roughly 8 miles or so)
     
    #3 robsnyder20, Feb 8, 2017
  4. Mendel Leisk

    Mendel Leisk EGR Fanatic

    Joined:
    Oct 17, 2010
    56,671
    39,221
    80
    Location:
    Greater Vancouver, British Columbia, Canada
    Vehicle:
    2010 Prius
    Model:
    Touring
    Think of it like an investment portfolio: don't sweat the momentary ups-and-downs.
     
    #4 Mendel Leisk, Feb 8, 2017
    RCO likes this.
  5. gher

    gher Junior Member

    Joined:
    Oct 10, 2016
    8
    11
    0
    Location:
    Tacoma WA
    Vehicle:
    2016 Prius
    Model:
    Three
    When going downhill like that in B mode, there is really no fuel going through the engine, it's just an air pump for resistance, so the instant mileage will read the same as if you were running purely electric. The max the mileage display will read is 199.9 MPG, so that's what you see since there was no fuel being used.

    I live about a half mile from my favorite grocery store, and when I drive to it in good weather after the car is warmed up the ICE never turns on, it's all electric the whole way, and my instant mileage shows as 199.9 MPG in that instance.
     
    #5 gher, Feb 9, 2017
    RCO likes this.
  6. RCO

    RCO Senior Member

    Joined:
    Aug 31, 2016
    3,709
    5,184
    0
    Location:
    Cornwall
    Vehicle:
    Other Hybrid
    Model:
    N/A
    Cornwall also has some steep roads and I have found that when you get this maximum mpg 199.9, once you start cruising again with ICE running or climbing another hill, the mpg soon begins to drop to a more realistic mpg.
     
    #6 RCO, Feb 10, 2017
  7. robsnyder20

    robsnyder20 Active Member

    Joined:
    Aug 13, 2012
    374
    301
    0
    Location:
    SW Florida USA
    Vehicle:
    2016 Prius
    Model:
    Three
    Thanks for your input everyone. I actually looked into it on other generation threads a few hours after posting and the consensus was that it used no fuel. I really liked using the DRCC for driving but didn't like how the engine would rev up for a normal stop. Now I know it doesn't use fuel when slowing down for a light.
     
    #7 robsnyder20, Feb 12, 2017
    RCO likes this.
(You must log in or sign up to post here.)