Modern engines run much cleaner. Some of it, as already stated, has to do with better air filter mediums. Most of it has to do with engine management systems that simply don't allow for the formation of the abrasive crud that older engines produced. Add to that the thinner oil in many newer vehicles (due to tighter manufacturing tolerances) and the much better blends of additives in modern oil and the filtration system no longer needs to be sized to collect a trash can's worth of big gritty particles.
That said, my oldest son and I collect military vehicles, mostly bigger stuff, that gets worked pretty hard on our farm, in our construction business and off road. Our medium and heavy trucks (and my F-350) are running either remote bypass oil filters or oil centrifuges for better filtration. Even with the older multi-fuel deuce and a halfs and the 230-400 HP Cummins engines the oil is still clear at oil change time...
Two of our multi-fuel trucks don't see the highway and live off road. They run on filtered waste motor oil and hydraulic fluid and still have clean motor oil.
Remote bypass filters are available for many pick-up truck and Jeep applications and they are cheap engine insurance. They filter a tiny bit of oil at any one time but do it to a much small particle size. Over a period of time all the oil gets filtered to a much cleaner state than a standard filter can provide. Most tap a small amount of the pressurized oil and return it by gravity and are pretty easy to mount.
Lance
