Question: what is the most fuel efficient marine diesel engine?
Answer: Caterpillar C8. ...  Caterpillar C12.9 Marine Diesel Engine. Caterpillar C18 Marine Diesel Engine. Caterpillar C32 Marine Diesel Engine. Cummins QSB 6.7 Marine Diesel Engine. Cummins QSC 8.3 Marine Diesel Engine. Cummins QSL 9 Marine Diesel Engine.