Yamaha 115 Lower-Unit Gear Oil: What to Use

The short answer

Yamaha 115 outboards use a hypoid marine gear oil in the lower unit (also called the gearcase). The grade generally associated with these motors is SAE 90. Yamaha sells its own marine gearcase lubricant under the Yamalube name, and that is the most direct way to match the factory specification. If you use another brand, it should be a marine-rated hypoid gear oil that meets the grade and service classification listed for your specific engine.

"Hypoid" describes the gear design in the lower unit, where the gears mesh under high sliding pressure. Hypoid gear oils contain extreme-pressure additives for that kind of load. "Marine-rated" means the oil is formulated for an environment where small amounts of water contamination are a known risk.

Why the exact model matters

"Yamaha 115" is not one engine. The label covers several generations and configurations built over many years, including two-stroke and four-stroke designs, standard-rotation and counter-rotating versions, and different shaft lengths. Gearcase oil type, required quantity and any model-specific notes can differ across these variants. Treat any general recommendation as a starting point and confirm it against the documentation for your engine.

Before buying or filling, confirm: • The engine model code and serial number, usually on the bracket or transom-clamp label; • The model year; • Whether it is a two-stroke or four-stroke; • Whether it is a standard or counter-rotating unit

What this guide does not specify

No verified source material was available for this article. For that reason it does not state lower-unit oil capacities, the required API service classification (such as GL-4 or GL-5), change intervals, or drain- and vent-screw torque values for any Yamaha 115 variant. These figures are model- and year-dependent. Take them from the owner's manual or service manual for your serial number, or confirm them with a Yamaha marine dealer.

Practical takeaway

For most owners, the simplest choice is Yamaha's own marine gearcase lubricant in the grade listed for the engine. If you use an alternative, match it to the manual on three points: hypoid type, SAE 90 or the grade the manual specifies, and the stated service classification. Confirming the exact model first prevents the most common mistake, which is applying one 115's specifications to a different generation.