The Honda 400EX (TRX400EX) typically uses SAE 10W-40 motorcycle engine oil that is compatible with wet clutches, such as Honda GN4 10W-40 or an equivalent oil meeting API SN or newer and JASO MA/MA2 specifications.
The 400EX is a four-stroke, air-cooled ATV with a wet clutch, so it needs motorcycle-engine oil rather than automotive oil. The exact grade and compatibility can vary slightly by year and climate, so always confirm with the owner's manual. Using an oil not designed for wet clutches or with friction modifiers can affect clutch performance and engine protection.
Official oil specifications and acceptable options
To choose the right oil for your 400EX, look for products that meet the following criteria:
- SAE grade: 10W-40 is standard for most ambient conditions.
- API service category: SN or newer (e.g., SM, SN+, or future equivalents).
- JASO specification: MA or MA2 to ensure compatibility with a wet clutch.
- Brand examples: Honda GN4 10W-40 is a longstanding Honda-recommended option; many high-quality motorcycle oils that meet the above specs are acceptable.
- Important caution: Avoid automotive engine oils and oils with friction modifiers designed for cars, which can cause clutch slippage in ATVs.
Choosing an oil that meets these specs helps protect both the engine and the wet clutch, especially under the demanding conditions ATVs face. Always refer to the manual for any year-specific notes.
Maintenance tips for changing the oil
Before outlining the oil-change steps, keep in mind best practices that help maintain performance and longevity:
- Warm up the engine to operating temperature to ensure complete drainage of old oil.
- Park on a level surface, shut off the engine, and remove the drain plug to drain the oil fully; replace the crush washer if needed.
- Replace the oil filter if your model has one, following the service manual’s guidance for your year.
- Fill with the correct amount and grade of oil specified for your model, then check the level with the dipstick or sight glass and adjust as necessary.
- Run the engine briefly, recheck for leaks, and verify the oil level once it settles; dispose of used oil responsibly.
Adhering to these steps and using the proper oil grade helps ensure reliable performance and protects the engine and clutch under typical ATV use.
Summary
In short, the Honda 400EX takes 10W-40 motorcycle engine oil that meets API SN or newer and JASO MA/MA2 specifications. Honda GN4 10W-40 is a common recommended option, but any equivalent motorcycle oil that meets these specs is suitable. Always consult your specific year’s manual for exact capacity and interval guidance, and avoid automotive oils with friction modifiers that can affect the wet clutch. Regular oil changes with the correct grade keep the ATV running smoothly in a variety of riding conditions.