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  1. #11
    Junior Member
    Join Date
    Dec 2007

    Heater effect on mileage

    As stated in the owners manual: The Prius gas engine runs continously when the engine is COLD. This wastes fuel and kills mileage, but is necessary. A gas engine must be at operating temperature or repeated starting and stopping will destroy the engine.

    In cold weather, when you use the heater you are drawing heat FROM THE ENGINE!!! The Prius engine is equipped with a coolant storage tank. This is what your heater uses to warm the cabin when the engine is not running, or running at very low power settings. But when running the heater in cold weather you are cooling the engine coolant, and sooner or later then engine has to start and run continously in order to bring the engine back up to operating temperature.

    The LESS you run the cabin heaters, the longer the engine stays at operating temperature (without running), and you get better mileage.

    In the summer, the AC unit draws electrical power from the propulsion battery requiring the car to waste fuel to recharge the battery, and supply energy to the AC unit.

    But before you shut off the AC... At expressway speeds, the aerodyamic drag from running 50+mph with the windows rolled down causes MORE lost power than running the AC unit. Especially in a very clean aerodynamic design like the Prius.

    Bottom line: If you want the abosolute best mileage, use the heat & AC sparingly. Do you really need to drive a sauna in the winter? Or an ice box in the summer?

    Quote Originally Posted by GreenGirl View Post
    I have Toyota Prius and I recently have been doing some observing of my driving habits to see how I can get the best mileage. In addition to the tips already posted on this site, here's another one that got my mileage to 50mpg. Don't use the heater!! Pretty simple one, and hasn't caused me any great inconvenience. If I just turn the dial to the highest temp, but don't turn the fan on, I still get a little warmed up. And I still get good gas mileage (even with my car fully loaded for camping!!!). I hardly use AC so turning off the heat has really increased my mileage to about 5mpg more!!!

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  3. #12

    got a question....is there

    got a question....is there any reason to turn on a/c when u use the heater?

  4. #13

    Cooling the air before

    Cooling the air before heating it removes some of the humidity, which is the reason that windows fog up.

  5. #14

    Before you get on your

    Before you get on your soapbox and tell everyone how stupid or lazy they are for not reading their owners manuals, perhaps you should research what you say BEFORE you say it. You kept saying dumb things like, "yada, yada, all electric, yada, yada" and "yada, yada, driven by electricity, yada, yada" and "yada, yada, no drag on the gas engine, yada, yada"... Do you think that a hybrid car is some sort of magic perpetual motion machine???? Gee, why don't they just put electric motors on the wheels and get rid of the gas engine altogether??? Do you think that they put some magic amount of "electricity" in the car when they build it to run the A/C, electric heater, lights and so forth? I suggest that you do a little re-reading of the science book you got in 7th grade - particularly the section about the 1st Law of Thermodynamics. I will paraphrase it for you in the same why that your 7th grade teacher did... "There is no such thing as a free lunch." Now, of course this, too, is obviously too complicated for you so I will dumb it down - but I'll let you find the error in your thinking by asking this question: Where do you think the "electricity" for the A/C and heater comes from???? Since you don't go to the GAS STATION and fill your tank with ELECTRICITY, do you think, that maybe, it comes from the gasoline that powers the engine that turns the generator (or the motor and is then regenerated by the brakes)? Maybe you should look at this article right here, on this site: http://www.hybridcars.com/gas-mileag...ditioning.html
    Then you can save the righteous indignation for sometime when you actually do your homework.

  6. #15
    Junior Member
    Join Date
    Dec 2007

    Now that

    Now that "dontlikeloudmouths" has proven he knows nothing about automotive technology, I'll post this for those who ACTUALLY have two working brain cells to rub together.

    The Prius (and other parallel hybrids) achieve high mileage and fuel efficiency by running the gasoline engine INTERMITTENTLY and ONLY at highest efficiency throttle settings.

    Gas engines are MOST fuel efficient when operating in the 60% to 85% load range. A gasoline engine operating at only 20% or 30% throttle gets HORRIBLE fuel efficiency.

    The Prius runs it's gas engine intermittently to both drive the car AND recharge the battery. And while the gas engine is running, the engine runs within the 60-85% throttle range when possible. The constant velocity transmission allows the engine to run anywhere from 1200 rpm to 3600rpm while the car maintains a constant speed on the highway. By running engine rpm independent of the car's highway speed, the throttle setting can be maintained within the 60-85% range except at the lowest and highest horsepower settings.

    When the Prius only needs a small amount of horsepower (cruising at city speeds) the gas engine is SHUT OFF, and the stored electricity in the battery drives the car.

    By using ONLY a 60hp gas engine, combined with the electric system, the Prius has the performance of a 140hp vehicle, with the fuel efficiency of a 60 hp vehicle.

    Am I going over your head "dontlikeloudmouths"? Do you need me to dumb these ideas down to your speed? How abut "Ugh- big motor bad, little motor good. Ughh, Ughh, Ughh".

  7. #16

    I'm still learning about

    I'm still learning about hybrid & electric vehicles in anticipation of a purchase, but I'm pretty sure that the lion's share of energy used in an A/C system is consumed by the compressor, not the fan.

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