Fuel Mileage - Automatic vs. Manual

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

  1. FloridaDudester

    FloridaDudester Light Load Member

    May 13, 2019
    I've always been a believer in Manual, whether its for sports cars or Semi Trucks. However, as I learned from on European sports car dealer, even an expert cannot compete with the electronically controlled automatic transmissions on the track. Then, I was at Select Trucks yesterday, and this elder salesman, thought very highly of the automatics. Since the majority of fleets are now autos, or some hybrid mix, it would be helpful to know the truths about modern (2015 and newer) trucks as it relates to fuel mileage, transmission type and then of course, how prone are they to breaking and the cost of repair.
    stillwurkin Thanks this.
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  3. stillwurkin

    stillwurkin Road Train Member

    Dec 2, 2017
    Well mpg depends on the driver, gross weight, and terrain. If all was equal i still say its hard to beat a good, smooth operator. I never used a big truck automatic so personally can't compare. But..for me standard is the way, as all in all i think much less trouble mechanically. I have witnessed 1 million mile transmissions. There again a % of that was the driver operating it. I am not against automatics, may even own one someday? I believe megas like automatics to eliminate chances on damage to the driveline. As probably most of their new drivers have trouble with a manual.
    FloridaDudester Thanks this.
  4. Rubber duck kw

    Rubber duck kw Road Train Member

    Dec 9, 2017
    You may get better mileage with an auto, but it only takes one electrical gremlin and you're stuck somewhere, also from the little I've heard and read they're more expensive to replace eventually when you need to.
    FloridaDudester and stillwurkin Thank this.
  5. Cattleman84

    Cattleman84 Road Train Member

    Nov 1, 2017
    The Sticks, Idaho
    Ive heard that some automated manuals are very expensive to replace... Some to the tune of $25k
    stillwurkin Thanks this.
  6. Brandt

    Brandt Road Train Member

    Sep 17, 2012
    The Detroit DT-12 auto shift has Ecoast. Mode. It will go into natural and coast when possible. It shift at the correct RPMs every time. So save a little fuel doing that. I think the biggest saving is, it's a direct drive transmission.

    It has some extra stuff like GPS location on the hills. So I change the shift point if going up hill. The transmission and engine talk to each other. The engine can turn on the Jake brakes between grease. So it never miss a grear when pulling a hill. When your at a stop line the computers will keep the brak pressure applied. Untill the truck starts to pull, so you don't roll back

    For fuel mileage you spec the entire truck for that. The direct drive transmission and rear ends. So the engine RPMs at low going 65mph.. My new company truck has the Smart Park electric a/c for sleep. So no idle time on engine. It getting 8.4 MPG with super single tire. I'm really impressed with the setup. Truck has 8 batteries vs 4. The 4 extra run the A/C at night and something like 250 or 275 amp alternator. To recharge the batteries going done the road
    stillwurkin and MartinFromBC Thank this.
  7. Ridlingdj

    Ridlingdj Medium Load Member

    Dec 12, 2018
    I'm sure autos probably get a bit better fuel mileage but I still believe that manual is better for reliably but if you have a ####ty driver that cant shift it will not last as long
  8. uncleal13

    uncleal13 Road Train Member

    Apr 9, 2009
    Humboldt, Sk
    A good driver will beat an auto shift hands down.
    However fleets cannot get very many good drivers so they purchase auto shifts to improve their odds.
    I have an auto shift now, I’ll be going back to a manual next time.
    My WesternStar 4900SF (not at all aerodynamic) got 0.2 better mpg than my Cascadia (aerodynamic) with an Eaton UltraShift.
  9. pushbroom

    pushbroom Road Train Member

    Sep 1, 2012
    Very good driver on a manual 18sp will beat out auto 18sp by a slim margin. Autos are easier to get then a good driver though
  10. stillwurkin

    stillwurkin Road Train Member

    Dec 2, 2017
    Thats a plenty of gadgets. The hand valve, or trolley brake ,whatever, is how we hold our truck on a hill as we let the clutch out. Lol. The fuel mpg is great. ( what, where, and how heavy)? Not a fan of super singles. Just about every time i pass a super single that is flat, the rim is ruined also. Not good $$ wise at least for me.
  11. shogun

    shogun Road Train Member

    Jan 23, 2009
    Doing a regen
    The DT12 is lights years ahead of the Eaton Ultra Snap POS. That transmission clunks every gear change and it sounds like it’s going to drop out of the truck.
    MartinFromBC Thanks this.
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