Special marine grade oil is needed for diesel marine engines, as they typically carry high loads for extended periods of time. The National Marine Manufacturers Association tests diesel engine oils and gives recommendations based on those tests. The oils tested may be entirely synthetic or partially synthetic.
NMMA-certified oils include: oil TC-W3 amalie, FC-W and FC-W (CAT). TC-W3 is used with two-stroke engines, FC-W with four-stroke engines, and FC-W(CAT) with four-stroke engines that have exhaust treatment catalyst systems. When selecting diesel oil, be sure to consider added characteristics