I drive busses for my school as a student job.. I got a free CDL out of it and get to pilot big diesels every day.. it is wonderful for me. Anyways, most of our busses are equipped with 5.9 Cummins, in both 12 and 24 valve versions. We also have a couple of bussed with 8.2 Detroits as well as a Cat (can't remember the model, but it is 360 HP), and 2 Sprinters.. a Dodge and a Freightliner.
Being ran 18 hours a day is hard on the engines, and actually, I have yet to see one die outright. We had one that had a tear in the inlet hose after the air cleaner, and months of driving through construction destroyed its rings until it let loose with one of them with me one night on the road, and it burned half of its oil capacity getting back to campus. Other than that and one of our 8.2s throwing a rod, we have never had a single one fail, and our mileage ranges from 12,000 on the Cat (It's in a 2003 Blue Bird Excel 102) to over 1,000,000 on a 1978 Blue Bird All American.
~D.J.~