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1600 mile mileage report

Discussion in 'Prius c Fuel Economy' started by tahoeRon, May 18, 2012.

  1. tahoeRon

    tahoeRon Junior Member

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    Vehicle:
    2012 Prius c
    Model:
    Two
    Just finished a 1600 mile trip, mostly at 65 mph. First, the overall results: On board display says 49.4 mpg. Calculated from gas fill-ups comes out 47.9 mpg.

    When traveling 70 or over, I was not able to beat 45 mpg. Headwinds make a difference, of course. My mpg dropped from 50 at 60 mph to about 43 at 72 mph.

    I ran the a/c about half the time, but could not see much difference in mpg. That may be because it runs off the battery, and that energy consumption doesn't register immediately. Temperatures on the trip ranged from the 70's to over 100 in the Southwest.

    I live at 6000+ feet and about half of the trip was above 4000 feet.
    The high elevation seemed to help the mpg, probably because the air is thinner and offers less resistance. The difference was quite noticable.

    I always purchase Chevon fuel, because I think it is better than some, and usually doesn't cost any more. By the way, fuel was lowest in Yuma, AZ ($3.79), Higher in San Diego ($4.39), and in between ($4.09) in Las Vegas.

    I have had zero problems with my Absolutely Red Prius C.
    The cruise control works the best I have ever seen. It pulled substantial mountain grades at 70 mph without any problem (unlike the 48 hp VW rabbit diesel I once owned).

    In summary, the mileage is substantially affected by speed over 65 mph, by winds and by altitude. The a/c must have a negative effect which I didn't quantify.

    Overall, very pleased.
    Ron
     
    #1 tahoeRon, May 18, 2012
  2. ProximalSuns

    ProximalSuns Senior Member

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    Altitude hurts mileage due to lower density and lower oxygen content of the air. That's likely why you averaged below the rated 52 mpg, the hills and the altitude.

    If you had no power issues, and were able to maintain speed going up the hills at that altitude, that's a good report for the C.
     
    #2 ProximalSuns, May 18, 2012
  3. PriusCinBlack

    PriusCinBlack Member

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    The air resistance due to speed is almost certainly most responsible for the lower mpg, however the above poster is also right about the lower oxygen content leading to worse combustion.

    Also, I've noticed that running the a/c does not lead to immediately noticeable decreases in mpg. But, it certainly does, and it can be dramatic, over the long term. I've noticed about 5-7 mpg decrease using the a/c, even on its lowest setting, over a trip.

    It's easier to notice your mpg creeping up after turning the a/c off, usually.
     
    #3 PriusCinBlack, May 18, 2012
  4. tahoeRon

    tahoeRon Junior Member

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    About that altitude thing... There is no question that less oxygen means that a gasoline engine has less maximum horsepower. The loss at my altitude is 15-20%.

    However, if the fuel mixture is adjusted properly, the resultant efficiency can be just as good. The Prius (and all modern cars)
    adjusts the mixture by using less fuel per gulp of air. I see no reason why the efficiency should suffer if the proper gas/oxygen ratio is maintained.

    Add to that the lower air resistance, and I still maintain that traveling at a high plateau (6000 ft) can yield better mpg that traveling at sea level. Look at jet planes... there is a reason they seek the high altitude.
    =====
    Ron
     
    #4 tahoeRon, May 18, 2012
    1 person likes this.
  5. ProximalSuns

    ProximalSuns Senior Member

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    Lower air density is as bad for airplanes as cars, any internal combustion engine. Airplanes have another problem with the lower air density as it reduces the lift of the wings requiring more power at the same time the lower air density reduces the engine output requiring more fuel.

    As for driving, the wind resistance at car altitudes up to 7,000 feet is likely not a major factor while the density consequences for the engine output, as you note up to 25%, are major. Turbocharging or supercharging the air intake is best way to overcome high altitude performance on engines but Prius do not have that feature. The electronic controls can lean out the mixture but this lowers the power per stroke and will lead to increased fuel consumption overall.

    Your numbers are good for high altitude, mountain driving.
     
    #5 ProximalSuns, May 18, 2012
  6. tahoeRon

    tahoeRon Junior Member

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    Well, I won't beat this one to death, but I think you are mixing up maximum engine power with combustion efficiency.

    Try a Google search on altitude and mileage efficiency, and you will find support for the high altitude advantage. Remember, this is what the Prius reported too.
    =====
    Ron
     
    #6 tahoeRon, May 18, 2012
    1 person likes this.
  7. F8L

    F8L Protecting Habitat & AG Lands

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    The AC hit is hard to read unless you have a numeric digital readout like on the Scangauge. I've performed various tests with the AC in my GenII then in my GenIII. The mpg hit averages 10mpg until the cabin cools down then may drop to only 1 or 2 mpg on a freeway trip. The hit could be much higher in stop and go traffic or if you are driving in 100F + with the AC maxed. The longer the trip the less of a negatively AC will affect mpg because you are not repeatedly cooling the cabin down and running the AC compressor hard.
     
    #7 F8L, May 19, 2012
  8. alfon

    alfon Senior Member

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    I too once owned a 1977 Diesel German Mfg
    Rabbit, 4 speed with 48 hp engine.

    I always got at least more than 50 mpg on cheaper than regular
    gas, # 2 diesel fuel which is all it required.

    In fact it was cheaper to run than my older 175 cc
    Honda Scrambler.

    It was a dog on hills but it seemed to run a lot
    better than my dad's Geo Metro XFI 3 cylinder
    manual tranny.
     
    #8 alfon, May 19, 2012
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