If youll look at Penske and Ryders Used Class 7 S/T truck sales sites, youll notice most of the trucks they sell have about 220K to 280K and there out of fleet use and up for sale, The have a term for it but its the HALF LIFE of the Engine, Drivetrain they feel before the truck starts needing repair and replacement of major items such as Turbos, EGR systems, Diesel Particulate Filters, etc...some trucks will run for many more miles before they need anything, some have far more need for parts, Ive read many Maintenance reports and the Mercedes 900 series seem to require the least parts, With the Cummins about the same, but the CAT falling far behind, most of the older CAT C7s need fuel injectiors, Pumps, and other parts replaced before the 200K mark....these trucks mostly all are fleet maintained, Have Coolant, Oil Samples done on each PM and fairly good records of Oil Changes etc....I think also it depends on how a trucks going to be used, will you drive from Texas to Michigan weekly, or from Detroit to Lexington and back....or even in the Northeast all thru the Stop and Go and SLOW of the cities. Proper Oils, Lubricants, Filters and Fuels have LOTS to do with the longevity of a diesel engine. Also Transmissions and Drivetrains, I do expediting and most of my Loads arent that heavy, I go from 8k to 1k loads and typically 4 K is the norm, so Im not overloading the vehicle or overworking the drivetrain if Im going up and down the Mountains and Poconos, etc. My fuel mileage stays pretty good and I keep my foot OFF the floor 90% of the time, using cruise where I can.
I had the benefit of taking diesel engines classes when I was younger and Ive always been into the mechanicals and maintenance end. One of the things I picked up on at the recent Expediters Expo was the mention of buying a grease gun and learning to Lube the truck, how to check all the fluids, knowing when fluids are worn out and need to be replaced, and to research the difference between Oils, Fluids Synthetic and Non, and coolants etc. I dont fall into the traps of some device with a turbonator that swills gas and gives 30% better fuel mileage....Clean air filters and Fuel filters do that well enough, Clean oil of the right viscosity, Lubes of the right viscosity, and even Wheel bearing Torque etc....its the little things that can give you LOTS more mileage.