Honda Gear Oil SAE 90 GL-4 – Genuine Outboard Gearcase Oil

Honda Gear Oil SAE 90 GL-4 is a premium gear lubricant designed for the lower gearboxes of Honda outboard engines. As a genuine Honda product, it is optimized to provide maximum performance and longevity for the transmission, maintaining your engine’s factory standards. The oil has a moderate level of EP additives (GL-4 class), which is sufficient to protect gears from wear without being overly aggressive to materials – ideal for the construction of Honda gearcases.

One of the key features of this oil is that it promotes smooth shifting of gears. In practice, you’ll notice easy and quiet engagement of forward, neutral, and reverse, as the oil minimizes friction between gears and clutch components. This is particularly beneficial during frequent maneuvers at the dock or while trolling, where shifting often occurs.

Honda SAE 90 GL-4 boasts excellent stability – its formulation resists oxidation and retains its lubricating properties during prolonged strain and heating of the gearbox. This means even after many hours of running, the oil remains effective in protecting components. The included corrosion inhibitors guard gear teeth, shafts, and bearings against rust and etching, which is critical in marine environments. Anti-foam properties ensure the oil does not aerate at high RPM, so every component stays coated with a continuous oil film.

This oil is suitable for both 2-stroke and 4-stroke Honda outboards – from the smallest 2.3 HP to the largest V6 models. It can also be used in the gearboxes of some inboard drives and bow thrusters where a GL-4 oil of SAE 90 is required. Using genuine Honda oil guarantees that the operation of the final drive (gearcase) is not compromised, preserving the smoothness and quietness characteristic of Honda engines.

Typical use cases:

• All Honda outboard engines (2-stroke and 4-stroke) – models from 2.3 HP up to 250+ HP – whose gearcases require SAE 90 GL-4 oil
• Annual transmission oil change during servicing of a Honda outboard – e.g., pre-season preparation or after 100 hours of operation, as per the manual
• Gearbox maintenance during extended operation in saltwater – Honda GL-4 oil provides extra protection against salt corrosion throughout the active season
• Boats with Honda engines used for leisure, fishing, or commercial purposes, where smooth shifting and long gearbox life are important
• Can be used in some inboard marine transmissions, thruster gearboxes, or other equipment if the manufacturer specifies SAE 90 GL-4 oil

Instructions for Changing and Use:

• Check your Honda engine manual for the recommended gear oil change interval (usually yearly or every 100 hrs). Have the required quantity of Honda SAE 90 GL-4 oil ready (1 liter is typically sufficient for most models up to 150 HP).
• To change the oil: keep the boat/engine vertical. Remove the lower drain plug on the gearcase, then the upper (vent) plug to let the old oil drain. Allow it to fully drain out.
• After draining, attach a pump with a fitting to the bottom hole and fill the oil from bottom to top. When fresh oil begins to flow out of the top vent with no air bubbles, install the top plug (with its gasket), then quickly remove the hose and install the bottom plug (with gasket). This ensures the gearcase has the correct amount of oil and no air pockets.
• Use new sealing washers (O-rings) on the drain plugs if specified to ensure a water-tight seal.
• After the change, always check for leaks – monitor the gearcase for signs of oil over the next few hours of operation.
• Tip: It’s best to change the oil after running the engine (while it’s warm) – warm oil carries out impurities more easily. Always tighten gearcase screws to the recommended torque (usually a few Nm – see manual).
• Do not substitute with GL-5 oil unless explicitly stated – Honda gearcases are designed for GL-4, which provides a balance of protection and material compatibility (e.g., with any bronze components). Using the genuine product gives you confidence in the correct chemistry and viscosity.