What kind of lower gear oil for mercury outboard 2 stroke motor?

For a Mercury outboard 2-stroke motor, it's recommended to use a high-quality lower unit gear oil specifically designed for marine applications. The typical choice is a 90-weight gear oil, such as Mercury's own High Performance Gear Lube or similar products that meet API GL-5 specifications. Always check your owner's manual for the exact specifications and recommendations for your specific model.