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Defrost and gas milage?

Discussion in 'Gen 2 Prius Fuel Economy' started by hdrygas, Jan 8, 2005.

  1. hdrygas

    hdrygas New Member

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    It got a little cold in the PNW over the past few days. In the past with my conventional auto I just kept my car in defrost mode for weeks at a time during the winter, so when it got cold I did the same thing and dropped my gas milage from high 40's- low 50's (48.5-50.5) on trips with a tank average around 49. Temps were in low 40's in the morning and high 40's to very low 50's. The Temps dropped to low 30's (29 one morning) and low 40's in the afternoon at best. I turned on my defrost as is my habit and left it on. I took a huge hit in mileage down to the low 40's with a last tank at 45.1 and only because I was really nursing the car and using every technique I have read about. I am afraid that I drove people crazy. I thought it was just the cold but yesterday I turned off the defrost and just had the auto set at 67. It was a bit warmer yesterday but not much 36-37 on the drive in and 42 in the afternoon. My milage took a big jump to the high 40's. I think it is at 49.5 with just 60 miles on a recent fill up. Does this make sense? Would using the defrost cause the ICE to run that much more? It was just one day and a bit warmer but I think the ICE was running much less often. I was actually driving around with out the CD or radio on just to listen for it. I am now going to experiment , I said it before and I say it again I wish I had the Mini Scanner. A secondary question is about the animation in the energy display. I don't think it always shows the ICE running when it is. I swear that I can hear and feel it when stopped and backing up and the display shows it off. Can anyone explain that? I am leaving the tunes off for a while and listen to the car.
     
  2. paprius4030

    paprius4030 My first Prius

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    Yes, the defrost does cause the ICE to run alot longer! But when you need the defrost what r u gonna do? I run the car in defrost alot but make sure the A/C light os off so the compressor doesn't run, that helps alittle i think. And your right about the ICE running and not being shown as running on the screen, I've noticed that too
     
  3. Tideland Prius

    Tideland Prius Moderator of the North
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    Defrost automatically turns on the A/C Compressor which may explain the mileage difference
     
  4. paprius4030

    paprius4030 My first Prius

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    Yes but then you can hit the A/C button again which turns off the compressor but it will still stay in the defrost mode
     
  5. hdrygas

    hdrygas New Member

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    Seems to me that what I need to avoid is just leaving it on defrost all the time. Turn it on defrost and go back to regular heat mode. I am going to experiment a bit more to get a better idea how it works. No need to be running the ICE if it is not absolutely necessary.
     
  6. Frank Hudon

    Frank Hudon Senior Member

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    Henry like us we gotta use defrost mode more than most because of the humidity. It's possible for the dealer to set "defrost without A/C" via the ScanTool the dealer has, it's a programmable option.
     
  7. DaveinOlyWA

    DaveinOlyWA 3rd Time was Solariffic!!

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    well one option would be after the windows are clear to crack the window a little. that will keep it from fogging up again.

    another option that i keep thinking im gonna try but keep forgeting to do, is rig a small electric fan up. i have one in my truck for defrost purposes but keep forgeting to get the fan. (its parked at my sisters house. i have assigned parking where i live and only have one space available)
     
  8. bruceha_2000

    bruceha_2000 Senior Member

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    Henry, You have to open the window and stick your head out to see, that way you don't need to run the defrost :)

    I use defrost to clear the windshield, then switch to defrost/foot mode and set the fan manually. I wish the voice mode understood 'Max Heat'. To force the electric heaters on in the AM, I say 85 degrees, then go to the climate screen, bump it one and set it to defrost/foot from auto A/C. kind of a pain, but not as bad as pressing the up button 20 times.
     
  9. victor

    victor New Member

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    Try saying "85 degrees" and then "warmer" or "hotter" to get that last step.
     
  10. Puzzler1

    Puzzler1 Junior Member

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    Hi all.

    I've seen many posts saying someone hits the up or down temp button 10 or 20 times to change temp. I've found that if you just hold it down, it keeps incrementing until it reaches the maximum hot or cold depending on the direction pressed. Is mine unique? I would be frustrated with having to press multiple times too!!
     
  11. jayman

    jayman Senior Member

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    The cold temps are brutal to fuel economy. At -35 C in city traffic, the motor always running, I "only" get 30 MPG U.S. gallon.

    At -35 C, there is no way in h*** I would turn the temp DOWN, or lower a window. Just not going to happen.
     
  12. canuckican

    canuckican New Member

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    Yup, I can confirm the MUCH higher gas use when defrosters are in operation. I have a 10-15 commute to/from work every day. With temps well below freezing, I run the defrosters usually all the way (the car has JUST warmed up by the time I'm arriving). The engine never shuts off at any stop regardless of the length of time of stop or how much pressure is applied to the brake pedal. At such times, my instantaneous fuel economy is 99.9 L/100km (the highest that can be displayed).

    needless to say, my fuel economy stinks this winter.

    As was stated earlier: Need the defrosters. Whatcha' gonna' do? As I've said before, I just content myself with the knowledge that I'm still doing better than I would in a "normal" car.
     
  13. rflagg

    rflagg Member

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    If you don't need to change the cabin temp, then your fuel economy doesn't need to suffer - just turn on the defroster, have it pull outside air, turn fan to lowest setting, turn a/c off. defroster will stay on, clear windows, and not run the a/c.

    If you're cold/hot, then that's a whole other ballgame. :)

    -m.
     
  14. jayman

    jayman Senior Member

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    Not at temps colder than -20 C does it work that way. You need close to max defrost airflow, and good heat, to keep the windshield clear. Especially at -35 C or colder.
     
  15. victor

    victor New Member

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    <div class='quotetop'>QUOTE(paprius4030\";p=\"62417)</div>
    I guess this has something to do with the which screen you are viewing. The one with the wheels shows how the power flows to/from the wheels. Then there is the consumption screen which shows the fuels used in 5 min segments.

    You will see the wheels stoped, and no fuel being used when you are stopped sometimes but the consumption screen still shows you are consuming gas. This to me makes sense since Im stopped but the A/C (for example) is causing the motor to run.
     
  16. hdrygas

    hdrygas New Member

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    I have given up on the energy monitor. I have turned off the radio and CD player, at great cost to my personal sanity, my tunes are life, for a bit to listen to my car and I have to say in cold weather the monitor has nothing to do with the ICE or at least as my ear can hear. I
    WANT A MINI MONITOR for this car.
     
  17. bookrats

    bookrats New Member

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    As a Puget Sound neighbor, I feel your pain.

    In Nov., I've had relatively low MPG -- low-to-mid 40s. Much of this is because I primarily use the Prius for short trips -- less than 10 miles at a time. This cuts down on the efficiency big-time.

    Combine that with having the heat/defrost blowers on all the time -- mid-to-high 30s this tank. Oh, well.

    For Seattle, though, this is probably the nadir of my gas mileage. Things will improve as the engine breaks in; and the temps around here will increase.

    The rental Prius I drove in September (with 12K miles on it) was in the 5x MPG all the time. I have faith that I'll see something similar by April.
     
  18. DaveinOlyWA

    DaveinOlyWA 3rd Time was Solariffic!!

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    you will. temps make a huge difference.

    roughly estimating from my stint of short trips i made while in a training class for 6 weeks just before winter formula gas, it takes about 2 miles or so for the car to warm up in fall, slightly less in summer im guessing.

    but when its cold like it has been the last few weeks, it appears to take about 6-7 miles to warm up. which now makes a 10 mile trip getting good mileage for about 30-40% of the trip instead of 80-85% of the trip that you see in summer.

    then add the 8-14% reduction in power for winter formula gas and most are lucky to see the 40's for mpg.
     
  19. quietman

    quietman New Member

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    ok guys have had my 2005 since jan 3rd and first thing i notices is that windows fog up much more than my 2002 prius did. i assume this is because it is bigger in side and it was very cold for the last two weeks. and of course the colder it gets the car works harder to stay warm and also got to break it in. my 2002 when i turned it back to the dealer, end of lease, was giving very good milage even when cold so i assume things will improve with the 2005 as i get miles on it. i love this car and take every chance i have to sing it praises. it has delivered everything i have expected of it and i hope the 2005 will also :D :guns: