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Overdrive Myth

Discussion in 'General Automotive' started by jgwheeler17, Oct 21, 2011.

  1. Oct 21, 2011 at 10:18 AM
    #1
    jgwheeler17

    jgwheeler17 [OP] I'm a zit. Get it?

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    so i have a question for those of you more knowledgeable to transmissions and towing. my roommate has an 06 f-150 (fx4 with the 5.4ltr for what it's worth) and when i was riding with him yesterday (not towing anything, just regular driving) he turned the overdrive off. i asked him why he did that and said

    him: "ive heard from a few people it helps save the transmission and get better gas mileage. i've been doing it about a week and i did get better gas mileage"

    me: "how does it give you better gas mileage exactly?"
    to which he proceeded to show me - as we were driving at about 45 mph he showed me how at that speed he was a steady 2,000 rpm(ish) and that when he got on the gas just a little it only went up to around 2,200.
    then he turned it off and the cruising rpm at that speed dropped to around 1,600 to which he applied the same amount of gas and it shot up to like 2,800 before descending back to 1,600 when it let off. he said..

    him: "see how when it just stays up there and doesn't jump real high when you gas it (with OD off), but when it's on and you gas it jumps up real high"

    me: "if you say so. i still don't know why cruising at a higher rpm to keep it from "jumping" when you gas it is gonna save you any gas like that since it's using more fuel to cruise than it needs to maintain that speed"

    My question is - from experience has anyone ever found this to be true? i can't see why in this day an age one of the biggest car manufactures in the world would make a truck that gets worse gas mileage in a non towing mode and how cruising at higher than required rpm will ever save gas.

    discuss. thanks.
     
  2. Oct 21, 2011 at 10:22 AM
    #2
    chris4x4

    chris4x4 With sufficient thrust, pigs fly just fine. Staff Member

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    Keeping it in OD gives the best MPG on our trucks. Fords are a strange vehicle, and the trannys' arent the most modern.
     
  3. Oct 21, 2011 at 10:24 AM
    #3
    jgwheeler17

    jgwheeler17 [OP] I'm a zit. Get it?

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    tint, dents, scratches, two blown speakers and trying to pay her off...
    hmmm. that's what i naturally thought. . . so do you think what he says makes any since or do you also suspect he might be an idiot?
     
  4. Oct 21, 2011 at 10:27 AM
    #4
    ink junky

    ink junky I phucking hate people >:(

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    Ok, I feel like a real dumb ass now! :laugh: but our 2nd gens have overdrive...? :confused:
     
  5. Oct 21, 2011 at 10:27 AM
    #5
    whippersnapper02

    whippersnapper02 Well-Known Member

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    It sounds like the convertor is locking when in OD. He should leave it in OD and learn to control throttle input better.
     
  6. Oct 21, 2011 at 10:28 AM
    #6
    chris4x4

    chris4x4 With sufficient thrust, pigs fly just fine. Staff Member

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    Any gear that has an ration lower than a 1:1 is considered an "Over Drive" gear, as it is rotating faster than the input. Some vehicles have 2 "over drives", while most 5 and 6 speed trannys have only 1.
     
  7. Oct 21, 2011 at 10:29 AM
    #7
    steve o 77

    steve o 77 braaap

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    I always turn the OD off in my mom's '94 suburban and her POS '07 F250. It seems to hunt for gears a lot less.
     
  8. Oct 21, 2011 at 10:29 AM
    #8
    chris4x4

    chris4x4 With sufficient thrust, pigs fly just fine. Staff Member

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    Your 5th gear is an "Over drive" gear.
     
  9. Oct 21, 2011 at 10:29 AM
    #9
    98tacoma27

    98tacoma27 :POOPCORN: Staff Member

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    I only disengage OD when towing on hills.
     
  10. Oct 21, 2011 at 10:29 AM
    #10
    steve o 77

    steve o 77 braaap

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    yeah you do, 4th gear is a 1:1 ratio and 5th (overdrive) is like .85:1 or something, not sure.
     
  11. Oct 21, 2011 at 10:30 AM
    #11
    maineah

    maineah Well-Known Member

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    Letting off the gas drops it out of lockup that's normal has nothing to do with O/D when he got back on the gas it locked up again that's also normal. O/D saves gas that's why it there it slows the engine that's a good thing. If it did not drop out of lockup when you let off the gas it would stall when you stopped at a light just like stopping with out pushing in the clutch.
     
  12. Oct 21, 2011 at 10:31 AM
    #12
    steve o 77

    steve o 77 braaap

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    you won't once you get some real tires on there :laugh:
     
  13. Oct 21, 2011 at 10:35 AM
    #13
    steve o 77

    steve o 77 braaap

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    lol

    when I had my 255's that 5th gear was right on the edge of being useless. It was still better up the hills than my roomates hardbody (on 29's lol) but still. Im regearing to 4.56 before putting another set of 33's on my truck.
     
  14. Oct 21, 2011 at 10:42 AM
    #14
    jgwheeler17

    jgwheeler17 [OP] I'm a zit. Get it?

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    maybe that has something to do with it.

    and that's a really good explanation of it. thanks.


    so has anyone else ever heard of the myth before now? i still think his "better gas mileage" might just be a placebo effect and that his knew found interest in overdrive being off all the time has just resulted in him driving more careful. also note, i don't know what his actual mileage figures are, im just taking his word for it. i know normally he only gets like 14 mpg.
     
  15. Oct 21, 2011 at 10:45 AM
    #15
    pootermobile

    pootermobile Well-Known Member

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    I have a 6 speed manual in my truck and once i got my ultragauge i noticed this: 6th gear at ~40 produces less instant mpg then 5th gear at ~40. I think its bc 6th gear being so low on the powerband, the little 4.0 struggles to keep the truck moving. Might be the same thing your f-150 buddy was talking about.
     
  16. Oct 21, 2011 at 10:55 AM
    #16
    Fiveology

    Fiveology Well-Known Member

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    This^^^^
    My company car is an 06 Expedition 5.4 auto (pretty much the same as your buddy's F150). The computer in these trucks wants to shift into and hold OD at such a low speed that the 5.4 (an engine that actually likes to rev, and has piss poor low end torque) really struggles to hold speed. Then if you want accelerate you really need to give it the boot to get a downshift or two. I usually drive around with OD locked out, and while I don't really track mileage since I am not paying to fill the tank, a tank seems to last just as long if not a bit longer with OD locked out, as it does with it on.
     
  17. Oct 21, 2011 at 11:02 AM
    #17
    jgwheeler17

    jgwheeler17 [OP] I'm a zit. Get it?

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    tint, dents, scratches, two blown speakers and trying to pay her off...
    very well explained. making a little more since now, thanks.
     
  18. Oct 21, 2011 at 11:05 AM
    #18
    Opihiman10

    Opihiman10 Active Member

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    Like everything else with re to engine control and whatever on most or all post 2000 vehicles, the transmission shift points are controled by a computer. The programs are designed to fit the needs of the vast majority of owners and give the best fuel economy.

    IMHO when humans think they are smarter at trying to get better fuel efficency, we usually end up pretty short. :D

    keeping his truck out of OD is likely not saving gas but probably helping to train him not to stomp on the gas as much.

    OPI
     
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