Diesel oil is designed and engineered specifically for diesel motors, should be purchased based on your engine rating needs. A Diesel engine works harder than a gasoline engine, because it works at higher temperatures. Typically marine oil should be changed every 100 hours, or sooner depending on how long the engine sits idle. Sierra Marine diesel engine oil, is formulated to protect your engine in a wide range of conditions. Meeting the highest standards of diesel oil in the marine industry and is certified to API CI-4+ rating.