How to Change the Oil in a 1990 Suzuki RM250: A Step–by–Step Guide

Shop parts for a 1990 Suzuki RM250 Dirt Bike.

Keeping your 1990 Suzuki RM250 in top shape means regular maintenance — and that includes routine transmission oil changes. Unlike four-strokes, your RM250’s engine oil is for the transmission and clutch only, as the premix lubricates the engine. Follow this proprietary MotoSport.com guide to safely, efficiently, and thoroughly change the transmission oil in your 1990 Suzuki RM250.

Tools and Supplies Needed

  • 10mm socket or wrench (for drain plug)
  • Allen key (for oil check bolt)
  • Rag or shop towels
  • Low-profile oil drain pan
  • Measuring cup (such as a Ratio Rite Cup, for adding new oil)
  • Fresh transmission oil (recommended: 10W-40 or Maxima MTL 80W transmission oil)
  • Torque wrench (optional, for correct bolt tightness)
  • Replacement crush washer (optional, but highly recommended)

Special Notes for the 1990 Suzuki RM250

  • This bike requires 10W-40 transmission oil for optimal clutch and gear lubrication.(Check your manual for capacity, usually around 750cc for this model.)
  • The drain plug is located directly under the transmission.
  • The oil check bolt is tucked behind the chain guard and wires, requiring removal of the guard to access it.

  • Do not over-tighten fasteners — aluminum threads can strip easily.

Step–by–Step Oil Change Procedure

  1. Warm Up the Engine (Optional but Recommended)
    • Let the bike idle for a few minutes to thin out the oil. This helps most of the old oil (and any contaminants) drain out.
  2. Place the Bike on a Stand
    • Keep the bike upright using a stand or have an assistant hold it. Place your drain pan under the transmission drain plug.
  3. Remove the Drain Plug
    • Use the 10mm socket/wrench to carefully loosen and remove the drain plug (underneath the engine, near the left side). Watch for hot oil.
  4. Remove the Oil Filler Cap
    • The filler cap is usually on the top left side of the engine case. Removing it will help oil drain more quickly.
  5. Let Oil Drain
    • Allow all oil to drain out. Tilt the bike side to side gently if needed to get the last drops out.
  6. Inspect and Reinstall the Drain Plug
    • Clean the drain plug and replace the crush washer if worn. Reinstall and finger-tighten, then snug with the wrench.
    • If you have a torque wrench, follow the specification in your owner's manual.
  7. Access the Oil Level Check Bolt
    • If your RM250 has the factory chain guard installed, remove it to reach the oil check bolt hidden behind the wires (left side, below the sprocket area).

    • Use an Allen key to loosen and remove the check bolt. This lets you verify oil level during refill.
  8. Add New Oil
    • Use a measuring cup to add fresh oil (typically around 750cc, but confirm in your manual for your RM250).
    • Pour slowly to avoid overfilling. Watch for oil to begin seeping from the check bolt hole—this indicates proper fill level.

  9. Reinstall the Oil Check Bolt and Cap
    • Once the proper level is reached, reinstall the oil check bolt (do not overtighten). Then replace the filler cap securely.
  10. Start and Inspect
    • Start the bike and let it idle briefly. Then turn it off and inspect for any leaks at the drain or fill points.
    • Recheck the oil level if required, topping up as needed.

Tips Specific to the 1990 Suzuki RM250

  • The oil check bolt location is often missed — be sure to remove the chain guard and look behind the wires.
  • Don’t overfill. Too much oil can lead to poor clutch performance.
  • Always use 10W-40 or a high-quality 80W transmission fluid designed for two-stroke transmissions. Avoid engine oils not specified for wet clutches, as they can cause clutch slippage.

  • Tighten bolts only to firm; the 1990 RM250’s engine cases are soft and can strip with excessive force.

Why Change Your RM250’s Transmission Oil Regularly?

  • Fresh oil ensures smooth shifting, maximizes clutch life, and protects transmission gears from wear.
  • Neglecting oil changes can result in gearbox damage and expensive repairs.

Conclusion

Routine oil changes are one of the easiest, most cost-effective ways to keep your 1990 Suzuki RM250 running strong. Using the right tools, proper oil, and following these steps gives you confidence and keeps your maintenance schedule on track.

Find all your tools, oils, and parts for vintage two-strokes at MotoSport.com.

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Disclaimer: This guide is provided for general informational purposes only and is not intended to replace your motorcycle's official owner's manual. Always refer to your manufacturer's documentation for model-specific instructions, torque specifications, safety procedures, and maintenance requirements. If you are unsure or inexperienced, consider seeking assistance from a qualified mechanic or technician.