Any oil carrying an API designation guarantees the fact that oil has met the specification requirements for its intended service. When servicing a diesel engine, the proper API designated oil must be used. During the combustion of diesel fuel a great amount of soot is generated. Some of the soot gets into the lubricating oil with the blow-by gases. This is the type of material that tends to plug oil filters.
Acids tend to form in diesel lube systems, caused by the combustion process and type of fuel burned.
These, too, can shorten the life of oil filters as well as cause corrosive wear. Raw fuel is more apt to get into the lube oil in diesel systems as compared to gasoline systems. The fuel dilutes the oil and affects its lubricity properties. The importance of lube system service is apparent. Specified service intervals, in fact, are usually shorter than those for gasoline engines.