Changing gear oil on an outboard motor is one of the easiest maintenance tasks a boat owner can perform. For years I let ours sit with the original oil that came with the engine, merely out of ignorance. Instead of taking the initiative and learning how to change the gear oil in the lower unit on this Yamaha 90, I ran it for 17 years with the original oil! For this 2007 Yamaha 90 Outboard Engine, the recommended oil is Yamalube SAE 90 gear oil. The bottle I used stated it was YamaLube Marine SAE 80W-90 Gear Oil and met GL-4 requirements. Both the vent plug and drain plug use the same "gasket" or washer and the part number is "90430-08020-00" which supersedes to "90430-08003" and I ordered them from Boats.net. I hope this video is helpful for you and if you have any questions, feel free to reach out in the comments!
