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MPG on a powerful engine with A/C on/off

Discussion in 'Technical Chat' started by bra, Mar 21, 2013.

  1. Mar 21, 2013 at 11:14 PM
    #1
    bra

    bra [OP] Well-Known Member

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    My dad got an old Ford F-250 7.3 v8 diesel 1992 and I'll use it during my working schedules only. He told me to use the A/C as I want because it won't affect the MPG. Indeed, he says that because the engine got huge torque...

    What do you think? I don't know if its théory is true.
     
  2. Mar 21, 2013 at 11:30 PM
    #2
    rickmeseke

    rickmeseke subaru of america

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    your dads on something good
     
  3. Mar 22, 2013 at 1:29 AM
    #3
    bra

    bra [OP] Well-Known Member

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    I found nothing about it on wikipédia
     
  4. Mar 22, 2013 at 1:40 AM
    #4
    S.B.

    S.B. Well-Known Member

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    I find no difference with my taco and also no difference with my dad's expedition 5.4L.
     
  5. Mar 22, 2013 at 9:20 PM
    #5
    bra

    bra [OP] Well-Known Member

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    I can't believe it, I'll try to compare with A/C on and off even if it is difficult lol
     
  6. Mar 22, 2013 at 10:32 PM
    #6
    worthywads

    worthywads Well-Known Member

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    Depends. Low speeds in town it will make a difference. If you are driving 80 and using a lot of gas already the addition of the A/C doesn't add much relatively.
     
  7. Mar 22, 2013 at 10:57 PM
    #7
    Rich91710

    Rich91710 Well-Known Member

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    This

    Under 40mph, leave it off and the window down.
    Above 40, AC on and windows up is a SLIGHT improvement... but it's not much.
     
  8. Aug 7, 2013 at 12:21 PM
    #8
    Smardt Turbocor

    Smardt Turbocor Older Guy

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    ===========

    Physics says the compressor uses from 5 - 15 HP to turn it over and compress or pump refrigerant. Your electrical blower (and the clutch on the compressor) increases the electrical load on the alternator making IT use more horsepower.

    I am personally still looking for perpetual motion machines and gas tanks that fill themselves magically. I have never found them.

    If your fuel mileage is not affected while using your AC then I may want to buy or steal your truck while you are sleeping at night.

    I do believe however that when not turned on, your AC will not affect fuel mileage.

    What your Dad may mean is that he doesn't detect any increase in fuel usage day to day, because he knows what it uses more or less each week, but then he probably hasn't mounted instrumentation to prove the compressor doesn't increase fuel consumption.

    Sorry, I just can't get away from the first and second laws of thermodynamics. They work and apply everywhere else.
     
  9. Aug 7, 2013 at 9:15 PM
    #9
    Rich91710

    Rich91710 Well-Known Member

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    Above 40mph, the load of the compressor uses less fuel than the drag created by open windows.
     
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