VW diesels used to scare the heck out of people every once in a while, the engine would start to run away, and turning off the key would not stop it.
Why? In serious blow-by situations in old engines, the motor oil would get entrained in the blow-by gases which are introduced into the intake manifold.
Cummins engines used to have an option called Centinel System. It was available for the M11 and later ISM. That system metered up to 0.3% of the crankcase oil into the fuel before the primary (filter before the lift pump). Oil changes with this system were defined by Cummins as being up to 75,000 miles depending on fuel mileage. Cummins dis post a Tech Service Bulletin stating that they did approve of up to 5% lube oil mix with fuel.
The problem is how do you mix it correctly. Dumping the oil into the tank and adding fuel does not have enough agitation with enough time to thoroughly disperse the oil throughout the fuel. Combustion of additives and minute wear particles is not an issue providing you have the correct filtration on the fuel system. Those filters will still remove particles at or above the micron rating of the filter.
Cummins discontinued offering the Centinel systrem when emissions laws in effect in 2007 called for catalyst mufflers and diesel particulate traps. Catalysts will foul faster when even small amounts of oil are burned. From an emissions point of view, the oil did not significantly change the quality of the exhaust.
