Difference between actual and reported panel consumption

Discussion in 'Gen 4 Prius Fuel Economy' started by Diego Sausen, Sep 28, 2019.

  1. GasperG

    GasperG Senior Member

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    I'm not talking about distance to empty, obviously the car doesn't know how you will drive in the future I'm talking about the MPG or l/100 km display in the car and hand calculated on the pump. As I said in Gen3 it was off by 6%-8%, looking at some data from Gen4 I would say the BC is not more 4% off.
     
  2. alanclarkeau

    alanclarkeau Senior Member

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    Sorry, what is BC?

    The DTE and MPG are related and compiled by the computer from the same data set - I've checked it a few times and have seen between 5% and 9% variances. On a long trip with few stops and relatively steady driving, the variance was smaller - normal short trips had a bigger variance - which is understandable as it's got more data to compile.

    I never bother checking it against reality - just use it as a guide - the real pump price/distance calculation is the valid one.
     
  3. GasperG

    GasperG Senior Member

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    BC - on board computer.

    DTE and MPG display are not related at all. DTE is more accurate if you do the same driving scenario every tank, MPG display in my experience is off by roughly the same percentage every time, no matter the driving style.
     
  4. alanclarkeau

    alanclarkeau Senior Member

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    No - DTE and MPG use the same data to compute them.

    I was reading on BMW and Mercedes FORUMS and they're saying the same - though it seemed that Merc was even more inaccurate.

    The bottom line is - they're just a guide. To get it 100% accurate, you'd be paying a lot more for the car.
     
  5. GasperG

    GasperG Senior Member

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    DTE uses past MPG data to predict the future
    MPG is only past data and obviously can be more accurate
     
  6. Diego Sausen

    Diego Sausen Junior Member

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    Hi guys, follow the post update.

    I fueled the car yesterday and it took 34.44 liters.

    So to run the 832.3 km (according to the partial odometer) I used 47.89 liters.

    Which gives an excellent average of 5.75l / 100km.

    Much closer to the average than the computer reports = 5.3l / 100km.

    Also very close to the margin of 7.5% ~ 8% difference between actual and estimated consumption by the car, as reported by other forum users.

    Thanks to everyone for the answers again.

    My spreadsheet is ready for the next supplies.

    One last piece of information:

    Yesterday before fueling, the range it showed on the dashboard was 94km.

    And as I explained in the first paragraph, there were still 8.56 liters left in the tank.

    I found a good margin of safety, because it is not common for him to make 9,10l / 100km.
     
  7. bisco

    bisco cookie crumbler

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    it does not take into account the safety margin
     
  8. Mendel Leisk

    Mendel Leisk Obtuse Angler

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    Interesting: Wayne Gerdes (CleanMPG website founder) had a pre-production 4th gen for testing, and he found the dash displayed mpg closely matched his calculations. It would seem they hadn't introduced the exaggeration factor yet.

    Just conflation Alan. The only thing preventing accurate dash displayed mpg is Toyota management.
     
  9. alanclarkeau

    alanclarkeau Senior Member

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    And BMW, FORD, SUBARU, MERCEDES, VW, AUDI, JAGUAR - all of them have similar discussions on their forums.
     
  10. Mendel Leisk

    Mendel Leisk Obtuse Angler

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    A couple of points:

    1. Our Honda Civic Hybrid was the first vehicle we had with mpg display. It was very consistant, either spot-on, or 0.1 pessimistic, in the liters per 100 km method.

    2. A ScanGauge hooked up to our Prius showed fuel economy that matched calculated. The car knows internally what the number is, but someone at Toyota wants the display to exaggerate.
     
    fuzzy1 and tucatz like this.
  11. Dave Lane

    Dave Lane New Member

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    I am late to this discussion, but with my 2018 Prius over 17000 km, I find that on average the car reports 6.9% better fuel economy than it actually gets from measured fuel as reported by the pump. It ranges from 5.4 to 9.1%.

    Your fuel economy does not seem that good (but maybe you are heavy footed!). My average (actual) is 4.7 l/100km over the whole period (and that includes a cold Canadian winter). See my other post is this forum dated September 3rd.

    Dave
     
  12. BAllanJ

    BAllanJ Active Member

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    Here in Ontario, pretty much all the gas is E10 (10% ethanol) and likely the Transport Canada (our EPA) are for just gas, so we shouldn't expect to agree there. Also, our gas pumps are "corrected" to 15C but the metering inside the Prius likely isn't, so that could cause some discrepancy.
    Also, I wonder how much the gas pumps can be off without them getting charged? I wouldn't put it past the gas companies to be pushing the limits as far as they can, especially with respect to their "correction" thermometers.
     
  13. mudworm

    mudworm Member

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    At >30k miles on my 2018 Prius, my calculated (real) overall MPG is 54.73 and the reported MPG is 57.40. Of course, it varies with each fill.
     
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