How to Change the Oil in a 2015 GAS GAS TXT PRO 125

Shop parts for a 2015 GAS GAS TXT PRO 125 Dirt Bike.

Changing the transmission oil on your 2015 GAS GAS TXT PRO 125 is essential maintenance for smooth shifting and extended engine life. This guide, proprietary to MotoSport.com, details all steps, the tools you'll need, and gives you model-specific callouts for a robust and successful oil change at home.

Tools and Supplies Needed

  • Socket set or spanner set (ensure metric, as GAS GAS hardware is metric-sized; check specifically for the drain plug and case bolts).
  • Drain pan (suitable for catching at least 1 liter of oil).
  • Clean shop rags.
  • Funnel (preferably with a flexible tip for tight spaces).
  • Measuring cup (for precise oil fill measurement).
  • New oil (recommended type: fully synthetic or semi-synthetic gear oil, e.g., NILS CLUTCH TRIAL, 370cc capacity as specified by the manufacturer).
  • Gloves (optional) to protect your hands from oil.

Preparation Steps

  • Ensure the bike is upright and stable, either on a stand or with assistance.
  • Warm up the engine briefly (2-3 minutes)–warm oil drains faster and carries more contaminants out.
  • Turn off the engine and let it stand for a couple of minutes so hot components are safe to touch.

Oil Change Procedure

  • Remove the drain plug:
    • Locate the transmission oil drain plug on the bottom of the right crankcase. Use the appropriate socket or spanner to loosen and remove it above the drain pan.
    • Allow all old oil to drain, gently tilting the bike if necessary. Inspect the oil for metal shavings or debris.
  • Replace and tighten the drain plug:
    • Wipe the drain plug and its seat with a clean shop rag. Hand-thread the plug back in and snug it with the wrench—not overtight, to avoid stripping the threads.
      Pro tip: Many owners and mechanics have reported stripped plugs on GAS GAS models due to over-torquing—be cautious. Snug is enough, oil is not under pressure.
  • Add new transmission oil:
    • Remove the transmission oil fill cap—usually located on the right engine cover.
    • Using a funnel, pour in exactly 370cc (or as specified on the clutch side of your engine) of the recommended synthetic or semi-synthetic gear oil.
    • Wipe up any spilled oil with a rag and reinstall the fill cap securely.
  • Check for leaks and clean up:
    • Start the engine and idle for 1-2 minutes. Check for leaks at the drain plug and fill cap. Shut off the engine and inspect the component areas again.
    • Dispose of the old oil responsibly at a hazardous waste or oil recycling center.

Model-Specific Notes for the 2015 GAS GAS TXT PRO 125

  • Oil Capacity: Always use exactly 370cc of transmission oil. Overfilling can cause excessive clutch drag, while underfilling can lead to damage.
  • Drain Plug Caution: The drain plug threads in the soft aluminum crankcase are known to strip easily if over-tightened. Use hand-tight plus a fraction of a turn, and never use an impact gun.
  • Oil Spec: Owners have success with specialty gear oils like GRO, Motul, or NILS CLUTCH TRIAL (see owner's manual for specifics), designed for wet clutch systems.
  • Ambient Temperature: On very cold days, warmed oil will flow more easily during draining and will also fill more accurately.
  • No Oil Filter: The TXT PRO 125 uses a wet clutch and gearbox oil setup—no engine oil filter is present, so frequent changes are critical for a long clutch and transmission life.

Recommended Oil Change Interval

  • For best performance and longevity, change your oil every 15-20 hours of riding or after especially heavy rides or competitions.

Conclusion

  • The 2015 GAS GAS TXT PRO 125 makes oil changes straightforward with a single drain and fill port. Take care not to over-tighten the drain plug, measure oil accurately, and enjoy smooth, crisp clutch feel and gear shifts ride after ride.

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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.