Fuel Mileage - Automatic vs. Manual

Discussion in 'Trucks [ Eighteen Wheelers ]' started by FloridaDudester, Jul 19, 2019.

  1. uncleal13

    uncleal13 Road Train Member

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    Saw pictures on the Detroit mechanics forum of the results of letting the Detroit AMT DT12 do its magic.
    Fellow just let it do it’s thing going down a mountain, at near 2500 rpm he heard a strange knocking sound, drove it to a a Freightliner shop. Had a connecting rod let go and punch a hole in the block.
    No warranty for driver abuse.
     
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  3. Snow Monster

    Snow Monster Medium Load Member

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    Howdy sonny, old driver here.
    Are you a troll?

    Might be way off base here, but I think most of us old farts got that AMT thing figured out pretty good.

    D is for make the truck go forward
    N means don't do nuthin
    R means go the other way

    A Chevy 2 speed auto from the 1950's was a little more complicated.

    P
    R
    N
    D
    L
     
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  4. Brandt

    Brandt Road Train Member

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    Yeah you have to watch the RPMs you will get a dash warning if you get the RPMs to high. You then have push the brake pedal and slow down. Sounds like that driver went higher then 2500. You get the warning about slowing down at like 2400 RPMs
     
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  5. Brandt

    Brandt Road Train Member

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    I'm was kinda joking a little, but these transmission will go downhill at 2,200 RPMs all day. It's programed when you turn on stage 3 Jake brakes to always keep the engine RPMs 1750-2,200. It will keep dropping gears to keep slowing truck down and always keep 1750-2200 RPMs for maximum engine braking. Most driver are not use to that.
     
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  6. Brandt

    Brandt Road Train Member

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    Another thing drivers do, is they turn the engine brake on and off as needed. When you do that on DT-12 transmission it will go into Ecoast. Then drivers say it not safe becuse it going down hill in neutral.

    You can't do it like that, you have leave the engine brake on all the way down hill. Then you have drivers using engine brake in the snow. Same thing they turn it on and off like regular transmission. Then they don't like how it drops a gear because I they say that unsafe in the snow or ice. When they should never use the engine brake in the snow or ice. But you could get alway with that in regular transmission.
     
    Last edited: Jul 21, 2019
  7. MartinFromBC

    MartinFromBC Road Train Member

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    My brother has a lot of them, I have just 6 Mack autos, many places in this area are using Mack or Volvo, and they have been extremely reliable. More reliable than most other brands, and there are multiple shops in the region that are great, who specialize in working on Mack and Volvo. The main independent shop in town works on all brands, he says that Mack and Volvo have been the best trucks as well, and he has been around a long time. And while I keep hearing about the engines eating injector cups on q regular basis, I have to wonder why only some have so many problems, yet they are few and far between here. We run heavier than trucks in the USA, and in our mountains we work the trucks really hard, we beat them in and out of logging roads while regularly grossing 130,000-210,000 pounds, and they just keep going. Maybe its because we don't spec our trucks to be all glitz and chrome for just rolling inter state highways, so possibly we skip whatever it is that causes some people issues. Here its 95% tri drive Mack Granites or Volvo VNX trucks. The other popular brand of truck is Western Star 4900 series trucks. Maybe we just maintain our trucks better, or who knows why, but dang the Macks and Volvos are tough trucks that just take a beating and keep on going.
     
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  8. bryan21384

    bryan21384 Road Train Member

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    It dont make a difference to me in terms of fuel mileage. Many people will vouch for manual because of what they are used to. Its really all the same. Its all in your rpms
     
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  9. MartinFromBC

    MartinFromBC Road Train Member

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    Interesting that the computer allowed that to happen.
    Automatics generally will not allow the engine to exceed redline.
     
  10. darknessesedge

    darknessesedge Medium Load Member

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    fleet im in the auto is always breaking down....
     
  11. MartinFromBC

    MartinFromBC Road Train Member

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    What brand of auto?
     
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