How to better mpg on Detroit 60Series?

It's not the engine, horsepower or driver. Your rear end ratio is where the problem is when comparing your 2 trucks. The 3.90 will give you better mileage running 90-95km/h where the other will have no problem running 105km/hr. The higher the ratio the lower the speed

 

4.5 years later.......?

 

1996 IH 9200 1,476,000 miles, motor rebuilt 30,000 miles ago, 3:90, 430/470 with the 485 program, 24.5 lp, 10 speed, flat bed around 80,000lbs out and empty back, 10' spread with lift axle on front axle when empty, 60mph on freeway, dual exhaust with flow through mufflers (walker mega flows) Mileage today checked with pencil and paper not dash display 8.93 mpg

 

No wonder why my t600 mpg is bad.

 

This post still going?
Might as well do an update.
We fixed the air leaks.
The other problem was a collapsing fuel line restricting fuel flow resulting in less power.
After we averaged 6-6.5 mpg

 

Other thing is Det 12.7 500 the best cruiseing speed for that engine with a 3.58 is between 68 and 72 mph
Under gross load of 79.800
Fuel milege will be between 6.3 to 6.8 mpg
That was with a eaton fuller super 10 speed?
You might get better with the 13 speed?

 

@the poet .....