The 1990 Honda FourTrax 300 uses SAE 10W-40 motorcycle oil in the engine and a separate 80W-90 gear oil in the drive/gearbox. Use API SG/SH or newer, and if your model has a wet-clutch, choose a clutch-friendly oil such as JASO MA/MA2. Always check the owner’s manual for exact capacities and any model-specific notes.
Beyond this quick answer, the article below explains where each oil goes, what specifications are most important, and how to choose the right oil for your climate and riding style.
Engine oil requirements
Before listing the recommended engine oils, keep in mind that the FourTrax 300’s engine is a four-stroke with a wet clutch, and the engine oil often also interacts with the transmission lubricants in this era. The following guidelines cover the typical engine oil for this model.
- Oil type and viscosity: SAE 10W-40 motorcycle oil (standard mineral or synthetic-blend is acceptable).
- Oil specification: API SG/SH or newer; for best compatibility with a wet clutch, consider oils labeled JASO MA/MA2 if available.
- Application: Engine oil only for the crankcase; do not mix in heavy gear-lubricant products in this compartment.
In practical terms, many riders choose a high-quality four-stroke motorcycle oil that meets the above specs and replace it according to their riding schedule and climate.
Gear oil (drive case) requirements
The FourTrax 300’s drive/gearbox in the 4x4 system uses a separate lubrication path that requires gear oil in the final-drive area. The following guidance covers the typical choice for this system.
- Oil type: 80W-90 GL-4 gear oil (suitable for motorcycle final-drive use). Avoid GL-5 unless explicitly approved by Honda for this model year.
- Compatibility: GL-4 is preferred to protect transmission synchronizers and gears in older Honda transmissions while remaining compatible with wet-clutch operation in many configurations.
- Capacity: Refer to the manual for the exact fill level and drain intervals; this can vary by drive configuration and year.
Using the recommended 80W-90 GL-4 gear oil in the drive case helps prevent gear wear and ensures smoother operation across temperature ranges.
Notes on oil selection and maintenance
Because this is an older model, some owners opt for synthetic blends or race-grade oils, but the key is to stay within Honda’s guidelines and avoid lubricants with excessive friction modifiers that could affect the wet clutch. Regular oil changes—more frequently in dusty or hot environments—help extend the life of the engine and drive components.
Summary
The 1990 Honda FourTrax 300 takes SAE 10W-40 motorcycle oil in the engine and a separate 80W-90 GL-4 gear oil in the drive case. Use API SG/SH or newer, and prioritize oils compatible with wet clutches if your model uses one. Always verify exact capacities and model-specific notes in the owner’s manual, as there can be variations across production runs.