How to Change the Coolant in a 2016 KTM 125SX

Shop parts for a 2016 KTM 125SX Dirt Bike.

Routine coolant changes are essential for the health and performance of your 2016 KTM 125SX. Fresh coolant helps regulate engine temperature, prevents overheating, and protects the internal components from corrosion–especially critical in high-revving motocross bikes like the 125SX. Follow this MotoSport-exclusive, step-by-step guide designed specifically for owners of this legendary two-stroke model.

What You Will Need

  • New coolant (check your manual for the recommended type)
  • Basin or container for old coolant
  • 8 mm socket or wrench
  • Funnel (recommended)
  • Torque wrench (preferred but optional)
  • Clean rag
  • Distilled water if you wish to flush the system

Preparation

  • Ensure the engine is completely cool before beginning to avoid burns from hot coolant or pressurized steam.
  • Stand the KTM 125SX upright on a stable surface. Place your catch basin under the water pump area.

Draining the Old Coolant

  • Locate the radiator cap on the left side of the handlebars. Remove it slowly to release any pressure.
  • Find the coolant drain bolt on the water pump cover. On KTM two-strokes, this is typically an 8 mm bolt at the lowest point of the water pump cover on the right side of the engine.2
  • With your catch pan in place, remove the drain bolt and allow all coolant to drain.
  • If you wish to flush the system, reinstall the drain bolt loosely, fill with distilled water, and repeat the draining process until only clean water exits.

Refilling the Coolant

  • Ensure the drain bolt and its copper washer are clean. Reinstall the bolt and tighten securely (recommended torque is 8–10 Nm for this bolt).
  • Pour the recommended coolant slowly into the radiator using a funnel. Fill up to the bottom of the filler neck to prevent air pockets. Gently tilt the bike side to side to help release trapped air.
  • If your 125SX has a coolant system bleed screw (some models do; it is generally on the radiator or thermostat housing), briefly loosen it as you pour in coolant until fluid runs bubble-free, then retighten.
  • Reinstall the radiator cap securely.

Final Steps

  • Start the engine and let it idle for a few minutes. Watch the coolant level—once the thermostat opens, the level might drop. Shut off the engine and let it cool, then top off coolant to the specified level if needed.
  • Check under the bike for any leaks, especially around the drain bolt and hose connections.
  • Add coolant to the expansion/overflow tank if your model is equipped, filling to the maximum mark.
  • Dispose of old coolant responsibly, following local environmental guidelines.

Key Notes for 2016 KTM 125SX Owners

  • The 2016 125SX features a lightweight aluminum radiator–never use plain water or substandard coolant, as this can cause corrosion and premature failure.
  • Always use coolant specified for high-performance motocross two-strokes. Ethylene glycol-based, silicate-free coolant is the manufacturer standard.
  • Check your radiator for mud or debris buildup before you change fluid. Keeping fins clean ensures maximum cooling efficiency.
  • It is wise to inspect radiator hoses and clamps for wear during coolant service–a blown hose can ruin a day at the track.

Proactive coolant maintenance ensures your KTM 125SX runs strong, from practice tracks to podium finishes. Keep up regular service intervals for consistent, race-winning performance.

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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.