Time to buy a new semitruck, but not sure what brand

I don’t think you’re reading my full posts. I’m just shy of 8.7 mpg. DEF cost is .01cpm, 1 penny a mile.
Those X15s aren’t getting over 7 at 95k gross. There are far too many examples of trucks at 80k or less hitting mid to upper 7s, and those are aero trucks with aero devices on the trailers. Tyson Foods buys a lot of Cummins powered KWs and they were getting 7.5 out of them. Knight Transportation buys a lot of Cummins powered LTs getting low 7s.
There are several people on this forum that have made multiple posts about their 389 with X15 getting only 5.8-6.3.
There was a recent study by PIT in Canada comparing KW, International, Freightliner, and Volvo on a test route in Canada to measure mpg. International and Freightliner were very close at 7.7 mpg at about 68k gross weight, aero trucks and skirts on trailers. The test route was a mix of flat and hilly terrain. The other brands were lower. So, if 7.7 was the best they got, trying for max mpg, in aero trucks, at 68k, and running downsped drivetrain, I’m supposed to believe that some Pete 389s with flat tops at 95k got over 7? C’mon man. The worst performer in their test was the Volvo at 7 mpg.
I don’t claim to know everything but when I read so many examples of what mpg those motors are getting and then someone chimes in with a scenario that’s much more intensive and with a style of truck that sucks fuel compared to the examples, and claims to be getting better mpg than those examples, it sounds a little fishy don’t you think?

 

Then the ECM's in all three trucks must be mis-reporting fuel usage then. Fleet numbers are lower overall because most of their drivers drive the trucks like cars, with the foot to the floor on acceleration and come to full stops at stop lights.

I've read countless posts on this website of owners getting over 7 mpg from their Series 60 Detroits in their big hood conventionals. I'm getting 5-5.5 right now with Canadian winter fuel running the truck all night. Just because you don't believe it, doesn't mean it isn't happening.

EDIT: Oh, totally forgot another good anecdote. Our most senior driver just got a brand new 567 last Christmas, 510/1750 Paccar, 18-speed Heritage Edition and was getting 6.65 mpg with B-trains in BC.

 

I will add regarding the old motors or pre emission. They are capable of very good fuel economy of you do some heavy modification and tuning. The guys at Pittsburgh Power have dozens of real world examples from 12.7s and 6nzs that they have modified and tuned for maximum efficiency. And, the guys that drive them responsibly are putting up impressive numbers hovering around 8 mpg in brick style trucks or aero trucks like a 386, T660, or Columbia. So I guess they are capable of the kind of performance I want if you have the time and resources to devote to that.

 

ECMs are definitely inaccurate. Any truck I’ve ever drove has been off by at least 5%. Even my current truck is not correct. When I talk about my personal fuel mileage it’s the actual gallons and miles, not the ECM.
It’s not that I don’t believe it, it’s that there are too many examples to the contrary backed by good data.

 

Different business models @Zeviander. I avg 6.5-7 running heavy city traffic in a brick truck. I could get 1mpg and make a profit (a lot less profit at that point, but profit nonetheless). If a business is set up to run 100-125,000 miles a year vs my 60-65k fuel mileage would likely make a much bigger impact one way or the other. Fuel cost me 8% of gross last year. It just isn’t nearly as much effect on my operation.

As for “Run illegal” etc
Yeah... year of the truck doesn’t determine if you run illegal: running illegal can be done in anything. Kinda sounds like people that argue gun control, that if there’s more laws, somehow criminals would follow the law. People running illegal logs, or speeding, or heavy- they’re already breaking the law, and aren’t bothered by it. What year the truck is don’t matter to someone that’s breaking the law.

 

I sill recommend the A26 over the Cummins but, if you must get Cummins I recommend the Endurant. Without knowing your tire size, I’d recommend a 2.64, that would give you 1150 rpm at 65mph.

 

I base my running illegal comment on the renewed interest in guys wanting 99 or older motors and the outrageous prices of used trucks that fit that description. It seems to indicate that there are still plenty of people that wish to run that way. There are other reasons to want a truck with an older motor and I think there is a lot of misinformation out there regarding the reliability of modern emissions motors.
It is within the power of a federal government to regulate air quality. I’d rather have emissions regulation than have to wear a mask over my face in an urban center as they do in China. Or, if you look at the air quality improvement in California in recent years, it’s hard to convince the public that emissions regulations are a bad thing. Gun control is a very different issue in that it’s not a resource shared in common as water, roads, air quality, or land is concerned.

 

I've got an international 9900 with an isx15 getting 4.4 us MPG pulling super B's over the Rockies every day.