How to Change the Oil in a 2015 GAS GAS TXT PRO 300

Shop parts for a 2015 GAS GAS TXT PRO 300 Dirt Bike.

Changing the transmission oil in your 2015 GAS GAS TXT PRO 300 is a vital maintenance task that ensures smooth gear shifts and long clutch life. This guide will walk you through the tools needed, specific steps, and essential call-outs unique to the TXT PRO 300 model to help you get the job done right, every time.

Tools and Supplies Needed

  • 8mm and 10mm spanner or socket set
  • Drain pan for old oil
  • Funnel for ease of refill
  • Clean rags or shop paper towels
  • Torque wrench (recommended for drain bolt)
  • 370cc of high-quality transmission oil (e.g., NILS Clutch Trial or a comparable 75W light gear oil)
  • Gloves (optional, for hand protection)

Preparation Steps

  • Start the engine and let it idle for 3–5 minutes to warm up the oil. Warm oil drains more completely and brings more contaminants with it.
  • Turn off the bike and position it upright on a stable stand for full drainage.
  • Wipe down the area around the drain plug to prevent debris from contaminating the engine during oil changes.

Oil Draining Procedure

  • Locate the oil drain plug on the right side of the crankcase, underneath the bike.
  • Place your drain pan directly beneath the oil drain plug.
  • Remove the oil filler cap (usually on the top of the clutch cover) to allow air in, so the oil drains quickly.
  • Use your spanner or socket to unscrew the oil drain bolt. Let the old oil drain completely—be patient and wait until the flow reduces to an occasional drip.
  • Inspect the drain plug for any metal shavings or debris. Clean the magnetic plug (if fitted) thoroughly.
  • Wipe down the threaded area before refitting, to ensure a good seal.

Reinstall the Drain Plug

  • Hand-thread the drain plug to avoid cross-threading.
  • Tighten the plug using your torque wrench to 23.5–25.5 Nm (17–19 lb-ft) to avoid overtightening and stripping threads. Do NOT overtighten; the cases are soft alloy. Over-tightening is a common cause of stripped drain plugs on trials bikes.

Refilling the Transmission Oil

  • Place a funnel in the oil filler opening for a mess-free pour.
  • Pour in exactly 370cc (check your measuring cup) of the recommended transmission oil. Using the right amount and type of oil is critical; overfilling can cause clutch drag, and underfilling can harm gear and clutch parts.
  • Replace the filler cap and wipe away any spills.

Special Model-Specific Notes for TXT PRO 300

  • Oil Type: Use a high-quality light gear oil. Many TXT riders prefer NILS Clutch Trial, GRO Gear oil, or an equivalent 75W SAE synthetic. Avoid using engine oils intended for four strokes; these can cause clutch slip or drag.
  • Clutch Feel: The 2015 TXT PRO 300 uses a diaphragm clutch with adjustable progressiveness unique to GAS GAS models. The right oil improves clutch bite and lever feel.
  • Oil Sight Glass: Some models have an oil sight glass on the side cover. After filling, let the bike sit upright and confirm the oil is at the correct level; it should settle between the max and min lines. If your bike only uses a fill quantity, stick to 370cc.
  • Drain Plug Location: Be careful not to confuse the oil drain bolt with the crankcase or coolant drains. Check your owner's manual or parts diagram as confirmation if you're unsure.
  • Sealing Washer: Inspect the copper crush washer or O-ring on the drain bolt. Replace it if it looks deformed or worn to avoid leaks. Never reuse a damaged washer.

Finishing Up and Post-change Checks

  • Start the engine and let it idle for a minute, then turn it off. Check for any leaks around the drain plug and filler cap.
  • Check the clutch function before riding—if the clutch feels different or has excessive drag, recheck your oil level and type.
  • Dispose of your old oil at a recycling center or local auto parts store.

Troubleshooting and Tips

  • If you stripped the drain plug, do not force it tight. Proper repair is a thread insert (Helicoil), not a bodge repair.
  • Always record your oil change interval and use fresh oil every 10–20 hours of riding, or after wet or muddy riding conditions.
  • Double-check the transmission oil spec in your manual if in doubt, as future updates may change recommendations.

MotoSport.com recommends following this exact procedure for maximum performance and longevity for your 2015 GAS GAS TXT PRO 300 transmission. For more parts, tools, and tips, visit our dirt bike technical guides or contact our support team.

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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.