Quicksilver - 15W-40 Heavy Duty Diesel Engine Oil 858042Q01. Overview. Marine diesel engines demand more than most. Long idle hours, tough loads, and salt-laden air test even the best systems. That's why Quicksilver 15W-40 Heavy Duty Diesel Engine Oil was built - to take on the challenges only the sea can throw at you. Whether you're powering a workboat or cruising for pleasure, this oil gives your diesel the endurance it needs and the reliability you depend on.. Key Features. Multi-grade 15W-40