....Also, the "engine hours" may be a better measure of life expectancy.
I have some 1,500 "hours" on my multifuel. It is furthermore not a linear accumulation of time, for lower rpms, the clock runs slower (it's tied in with engine rpm).
So, say that at highway speeds it should be more like 2,000 hours and to compare "highway speed" with an OTR tractor trailer rig, we should probably use 70 mph. So in conclusion, my 1,500 engine hours may be the equivalent of 140,000 miles for a commercial OTR rig and my engine isn't even breathing hard.
Many factors and definitions to consider here....