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84 mpg with cruise control

Discussion in 'Gen 3 Prius Fuel Economy' started by zebekias, Aug 12, 2014.

  1. DoubleDAZ

    DoubleDAZ Senior Member

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    Duh, I didn't think in terms of altitude, I was more concerned with the time and distance I have the brakes on. :) I haven't driven the hills I'm talking about in the Prius yet, but I had to ride the brakes in my van. I'll keep an eye on the battery meter to see what happens with it. Thanks for clarifying.
     
  2. priusdonkey

    priusdonkey Member

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    down hill, with a tail wind will get you 84mpg. i drive from Tehachapi, CA to Mojave, CA and it is around 30 miles, i can get 99mpg at freeway speeds, less going uphill with a headwind. like the saying goes - "there are no free lunches"
     
  3. zebekias

    zebekias Member

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    The drop on your route is 370 meters! My drop is 103 meters. I'll soon do the route in reverse.
     
  4. Mendel Leisk

    Mendel Leisk Senior Member

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    And with all the numbers being kicked around, you need to deduct 5~10% due to the dash display's meter positive bias.

    Our meter's sitting at 2.6 (liters per 100 km) right now. Doesn't mean much: I just refilled/reset at the top of a very long downhill, followed by easy highway, fully warmed and lowish speed. Over the next few days it'll get back to normal.
     
    #24 Mendel Leisk, Aug 18, 2014
    Last edited: Aug 18, 2014
  5. zebekias

    zebekias Member

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    Today I did the same route, but this time in both directions, however, it was unusually cooler at around 25 C.
    At the end the car displayed 3.5 l/100 km or 67 mpg. It was mostly done via CC.

    I learned some new things:

    When the SOC is high, the car can go pure electric up to 87 kph.
    When the SOC is average, the car will go pure electric up to 77 kph.
    When the SOC is low, the car may kick out of electric even at low loads around 67 kph.

    When the car is fully warmed up, the car can go most consistently on pure electric up to 77 kph, so setting the CC at exactly 77 kph may be advantageous. This is what I did for most of the trip. Although I experimented going 90 kph at some sections and the average consumption did not go up. Tomorrow I'll experiment doing the round trip at 90 kph to see what kind of consumption I get.
     
  6. Mendel Leisk

    Mendel Leisk Senior Member

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    It's pretty much a given that higher speeds will cut your mpg. 90 kmh doesn't cut too deep though.
     
  7. priusdonkey

    priusdonkey Member

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    There is only so much economy that you can squeeze out of the engine/car. At speeds of 65+mph aerodynamics plays a big part. The prius was designed in a wind tunnel, but you can't overcome drag in the form of parasitic and skin friction and the frontal surface area. The Prius is a slippery vehicle with a low coefficient of drag, but drag nonetheless. My guess is you could probably trim half the weight of the vehicle by using exotic composites, aluminum subframe, hydrogen fuel cells and creating a two seat version. Stick some wings on it and you could fly your EV over the traffic on the 405 freeway and bust Bravo airspace.
     
    Robert Holt likes this.
  8. zebekias

    zebekias Member

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    I just did the same route again, but it was a cool 21C going (8am) and 24C going back (9:30am). I just set the CC to 80 kph. Just prior to leaving in the morning I set the tires to 42psi front and 40psi rear. Result:

    3.5 l/100km or 67 mpg.

    On the highway I seem to get 67 mpg consistently without any effort on my part so long I stick to 80kph. I really don't see the point going 90kph, you don't gain much.
     
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  9. Mendel Leisk

    Mendel Leisk Senior Member

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    ^ Are these numbers the car's telling you? 'Cause Toyota's insistance on exaggeration makes for some confusing discussions.
     
  10. zebekias

    zebekias Member

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    Yes! I have yet to determine the accuracy of the FE indicator, but I did remember to zero the 'A' trip odo after my last fill-up so I can go fill up at any time and see how many liters it takes in.

     
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  11. zebekias

    zebekias Member

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    One important detail I forgot to mention is that our gas here is 100% pure gasoline. It better be, for $8/gal lol.
     
    #31 zebekias, Aug 31, 2014
    Last edited: Aug 31, 2014
  12. zebekias

    zebekias Member

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    Today I did highway driving at 100 kph with CC! I never disengaged it. I noticed when the HSI shows a medium to low load (needle at or below slightly above the mid-level) the instantaneous consumption is some insane number, 1.x or 2.x l / 100 km. That's pure ICE, no indicated electric assist (unless the display lies.) I'm starting to reconsider the wisdom of always going no faster than 80 kph. My FE did not get any worse! LOL
     
  13. Starship_Enterprius

    Starship_Enterprius Active Member

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    zebekias, i've been noticing the same with my CC. So i tried driving without the CC and doing SHM by staying longer in those 1.x or 2.x areas and i got my best FE readout so far (3.6l/100km).
     
  14. zebekias

    zebekias Member

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    I finally calculated my fuel efficiency. I did 697.8 km using 29.67 l which comes to 4.25 l/100 km vs an indicated 4.0 l/100 km. So the computer is around 6% optimistic. Note that several factors have contributed to the worse FE number for this tank.

    1. It has gotten a lot cooler, gone are the 40c days, we are now in the 20s.
    2. I decided to increase my highway cruising from 80 to 100 kph.
    3. I no longer do anything special on the highway, I set the CC to 100 kph and let car sort things out.
    4. I've been doing lots of short (<6km) trips.
    Considering the above 55 mpg is not bad.
     
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  15. zebekias

    zebekias Member

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    By the way, to get these great numbers I noticed the car must be fully warmed up. It takes around 10-15 mins.
     
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  16. priusdonkey

    priusdonkey Member

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    in SoCal we drive over 80-90kph on the surface roads. Highway speeds are 70-80MPH, Rush hour traffic is 8mph and is mostly just stop and go. Yes i notice the best FE/Cruising speed at around 55MPH. It is just not worth the extra time to squeeze 3 more mpg and drive for an extra 12 minutes...

    In SoCal summers the engine warms up quickly 3 minutes? i would think that would hold true in Greece.
     
  17. zebekias

    zebekias Member

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    I have given up on 80kph, I usually drive at 90 or 100 kph on the highway now. Instead of 3.5 l / 100 km I get 3.7 to 4.0 depending on temperature. It takes roughly 50 seconds for the first stage warmup, and about 10 km of 80 kph driving to be fully warmed up to the point it goes into SHM on the highway.
     
  18. SageBrush

    SageBrush Senior Member

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    The old mantra used to be "60 mpg at 60 mph." In metric that would be 3.9l/100km at ~ 97 kph.

    Sounds like your car came from the same factory as ours ;)

    I have to drive my Prius v(agon) at 85 - 90 kph to manage 60 mpg -- and I am aided by driving at altitude of 6000 - 7000 ft.
     
  19. zebekias

    zebekias Member

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    60 on 60 is pretty accurate. Right now with the temps in the low 20s C here it may be achievable on the highway when fully warmed up. However, including the many short trips I take and the 6% indicated FE optimism I'm getting actual 54 mpg.