Fuel Mileage - Automatic vs. Manual

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

  1. Rubber duck kw

    Rubber duck kw Road Train Member

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    Automatic trannys just enable the simple who shouldn't drive cars to drive a truck, they're also a good part of the reason you see people doing 25 mph through the truck stop.
     
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  3. stillwurkin

    stillwurkin Road Train Member

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    My ooh my ...LOL
     
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  4. x1Heavy

    x1Heavy Road Train Member

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    My auto bricked TWICE. It's a rockwell meritor automatic and we were a team truck. We read in the manual that the truck requires 1 hour every seven days to shut off. So it can flush the buffer. But we never shut off. Not even for 5 minutes. So it bricked twice.

    I am a manual man until the day I die. However there were two other demonstrations that automatic did for us. One would be eastbound on I-70 at the Colorado-Kansas Border racing a summer storm front that was faster than we were. And the fuel mileage on the truck got about 7.8 or so until the front reached us. It started pushing on the trailer like a sail and we started seeing 15-18 or higher spikes of MPG.

    The other demonstration was wife enduring her first tractor jackknife on ice west of Knoxville on I-70 going west. We were number one in Convoy of about 7 trucks. All of us rolling nicely. Not much talking. she hit that ice on a curve to the left upgrade steeper and in the shade was where that ice hit us. Tractor slipped like a fat lady on a stack of marbles and was about to throw the whole thing into the median in the middle. I hopped onto the dash board and moved her wheel 4 inches and held fast frozen telling her to hold everything, essentially freeze. The truck and transmission dug back into good traction and then the transmission found a gear and settled us down to pull out of that horrible jackknife.

    Number two hit and came out ok. Three went into the median backwards to hold his flatbed load up. Everyone teaches you not to try to use your drives and horsepower to try to break a jackknife. But this driver was doing that to hold it straight as the whole thing fell into the canyon. 4 through 7 cursed up a storm. But no one was hurt. Eastbound started yelling as well.

    We proceeded at interlock and 8 to 14 mph all the way to Memphis. Which was the end of the winter storm that day. Once in Arkansas it's dry, open her up and let her run.

    If that was a manual we would have gone into the middle and then rolled once she stalled out on us. So its a good impression for a auto.

    Today's autos in some ways require a satellite to tell it when to down shift for a upgrade. To me that's over engineered BS. Some autos probably will get you killed in ice and snow in certain mountain passes. How? It only knows how to upshift. The minute it thinks you are going fast enough, it will upshift on you. All of the winter knowledge and experience out the window in favor of a suicide transmission that again was programmed by engineers who never see the mountain snow.

    (Solution) make sure your auto has a manual paddle mode. That way you can pick one gear up and down the whole thing in mountain driving.

    We are going to probably have to by and run Robot trucks. It will be over my dead body. But I am getting to where I think Robot trucks will be necessary because a growing percentage of drivers do not possess the necessary skills to do anything right in trucking.
     
  5. uncleal13

    uncleal13 Road Train Member

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    What sort of rpm ranges do they operate in. A few of our guys have Volvo’s and the eat injectors all the time. The D16 was prone to it, but even the newest D13’s are doing it too.
    140,000 lbs super-b train hopper bottom on the Canadian Prairies.
     
  6. MartinFromBC

    MartinFromBC Road Train Member

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    Macks and Volvos share a common engine and transmission, despite their different names. Generally speaking because most here haul heavy loads, and in severe mountain terrain, they order heavy duty trucks, set up to haul heavy, and the transmission is programmed to keep it in the meat of the power once the driver has stepped down to 90% plus throttle. My Macks will cruise if empty and on flat ground around 950 to 1300 rpm usually...but add some weight and start opening up the throttle it will downshift at about 1150 to 1250 rpm, and if accelerating will spin her up to around 1500 to 1700 depending upon how hard and how long you are making it pull. I was at 192,000 lbs gross a few weeks ago and she had to pull up the hwy 24 hill, i timed it for how long i just left it flat to the floor, and it was 19 minutes later I eased off the throttle some. It stayed between 1200 and 1700 rpm the entire time. Nothing got hot, it just pulls, and pulls! These injector problems i keep reading about are still a mystery to me. I only read about them on the internet, don't experience any myself. Regardless of what happens, when the engines need a full overhaul I will have the injectors replaced at the same time.
     
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  7. Matt1924

    Matt1924 Light Load Member

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    Only automatic I've driven has been that volvo ishift 12spd. I'll tell ya, that thing doesn't know when to shift, plus it lagged so much. Kinda made driving scary that it wouldn't respond for a second or two after you pressed the throttle. My thought is that a good operator could get similar or comparable mpg vs an autoshift contraption. Also, I enjoy shifting and having ultimate control. A safety issue for me, as well as enjoyment.
     
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  8. FloridaDudester

    FloridaDudester Light Load Member

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  9. FloridaDudester

    FloridaDudester Light Load Member

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    I thought that all autos have the capability of manually shifting up or down and that the auto transmission then adjusts to that input, or learns your driving style. Perhaps not.

    Your commentary is very helpful. I'm mostly concerned about their longevity and whether they really are so good at shifting that the autos give consistently better fuel mileage than 10 or 13 speed manuals. It's good to know they can also help save lives in a pickle, as you described.
     
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  10. MartinFromBC

    MartinFromBC Road Train Member

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    You can select the gear yourself, very rarely do I though. It does a really great job on its own.
    What it doesn't allow is for you to select a gear so low it will over rev the engine. If you're cruising down the hwy in say 14th gear, and try to tell it to drop to 7th, it simply won't do it, knowing that it would grenade the engine. Most of the time if I do lock into a gear, its descending a steep hill, and I want the rpm to stay up for more engine braking. So say I lock it into 7th gear, i just use enough braking to keep the rpm down to say 1800. I had not driven an automatic transmission class 8 truck until 2 years ago, my first 32 years I only drove a manual transmission. I have many drivers who have been driving semi trucks for 20, 30, and almost 40 years for the one guy, and since I got 6 Macks with automatic, all of them love the automatic. I can choose from a variety of trucks, and I prefer the automatic over my 13, 15, and 18 speed manuals. Honestly i have never understood the 18 speed, I don't split the lower gears anyway.

    I should add that I do not have the highway cruiser trucks, my Macks are the 14 speed, not 12 or 13 speed ones also available. Those crawler gears are sure nice to have when lifting off in soft ground and its a 15% grade your stopped on, and the gross is say 180,000 lbs. I just select crawler gear 1 and gently apply throttle, it just lifts off with ease and upshifts perfectly. Less chance of spinning out to. My future will have more Mack trucks with autos in them guaranteed. Soon time to decide how many more Macks to order, and what options I want that aren't in the 6 used ones i bought already. I used to be a die hard Kenworth guy, but not anymore. Open offer to you, come on up for a visit sometime, ride with me and my drivers for a few days, see them in action, then decide. My grizzled old timers were totally against the mere idea of an automatic truck. My very first driver I ever hired is still with me, he is stubborn and set in his ways. He balked at them new fangled 18 speeds, thought real trucks only had a 15 speed, and I said listen you grumpy old bugger drive it....he eventually didn't hate the 18 speeds. Well when I bought some automatics he was all about how they sucked and why did i buy them. So I made him drive truck one the day after I got it here. He left all cranky that morning about having to drive it...when he came back that night he got out of the truck, walked up to me, and asked if he could have it again the next day. He was sold on how great it works, and now he drives one about 90% of the time, and curses the stupid old manual shift trucks lol. I guess that compared to some old men I can adapt quicker to things, and am more open minded. Every driver I have learned on a stick or two sticks, and zero had any experience with an automatic until i got my Macks a couple of years ago. Now everyone of them, and myself, prefers the automatic. My sore shoulder really appreciates it a lot.
     
    Last edited: Jul 21, 2019
  11. FloridaDudester

    FloridaDudester Light Load Member

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    Really nice information on the acceptance of the autos. I'm about convinced I don't want any type of manual transmissions, car or truck. I hope to hear more guys chime in and bragging about their automatics.

    Thanks
     
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