Oil analysis for a crosshead type diesel engine indicates the TBN of the crankcase lubricating oil is increasing. This is most likely associated with which of the following?

Correct Answer: Option C — Leaking stuffing boxes introducing cylinder lubricating oil into the crankcase

In large crosshead diesels, trunk-type cylinder oils possess a high Total Base Number (TBN) to neutralize corrosive combustion acids. When crankcase oil TBN mysteriously rises, it indicates high-alkalinity cylinder oil from leaking piston rod stuffing boxes is contaminating the lower crankcase sump.