Automatic vs manual mpg

I'm in a 12' KW 660 getting around 7.6mpg 10speed

 

I drove a 2012 cascadia with 10 sp, going 68 mph, and gets 7.9 mpg. When cruising on us route 30 in oh at 64 mph, it gets 8.4 mpg.

 

The bold is why the automatic is said to get better fuel economy. It is designed to shift when needed to keep the engine rpm and torque in spec for the best fuel usage not always the best speed up the hill. It takes extra fuel to maintain speed, which you will give it in a manual by controlling the gears to achieve maximum speed, not always the best fuel economy. An automatic will beat a manual for fuel most of the time, it takes a really skilled and disciplined driver to maximize their fuel economy, an automatic does this for most drivers.

 

In a car application a manual trans always did better because of the slippage involved. They came out with lockup converters to take care of the slippage in high gear. Like brian991219 said it takes a skilled driver too maximize fuel economy and know the torque sweet spot of his engine.

 

My smart shift does all kinds of stupid things to kill my fuel economy. Runs the engine up to 2200rpms and sits it there, takes 8-15 tries at revmatching a gear when shifting, shifts back and forth between gears uphill, and keeps the engine in gear while stopping and downshifting until 4th gear.

I was a disciplined driver in a manual, getting 7.1-7.5mpg regularly in a dpf truck, but this piece of junk has been doing 5.5 mpg lifetime, and anywhere from 4.4-6.9mpg on paper. Breakdowns from the transmission alone have run me about $1500 a year as well.

 

That "auto shift will get better mpg than a manual" assumes typical fleet type of driver. For an experienced driver who really pays attention to how they do things, I think it is a wash. A good driver tries to understand the power curve of their engine and find where it does its best work at the best mpg. It is mostly a selling/marketing thing put out by the OEM's to state that auto shifts will always get better mpg. Remember, they are primarily targeting fleets with this marketing stuff.

And the auto shift has limits. It has to be programmed to take full advantage of the engine, loads and conditions. Many just take the truck out and drive it and have fits over where the auto shifts and such. It needs to be taken in and have shift points reset to where they need to be and other settings. A auto shift has over 100 parameters that can be set to adjust things where they need to be. Like most things, the factory just sets stuff at a basic level and ships it.

 

I was a 2nd year driver getting 7.0 in a 2010 KW with a 485 Cummins 13spd, running 65-68 pulling most of the time 42K+. Companies stop being cheap and spec it out right you could run highway speeds and still get good fuel mileage.

 

My T600 is not just an ordinary fleet truck. Had 475 hp, 10 sp, and 3.70 rear axles. Tuned up to 500 hp and runs like a champ but one thing sucks that is stock mbn, turbo, 10 sp, killer muffler, and has 3.70.