How to Change the Coolant in a 2009 KTM 125SX

Shop parts for a 2009 KTM 125SX Dirt Bike.

Changing the coolant in your 2009 KTM 125SX is an essential maintenance task that helps keep your two-stroke engine running at top performance and protects it from overheating and corrosion. Here is a step-by-step guide tailored specifically for 2009 KTM 125SX owners, including model-specific notes you need to know for hassle-free coolant maintenance.

What You Will Need

  • Fresh motorcycle-approved coolant (avoid using automotive-only antifreeze)
  • Drain pan or catch container
  • 8mm socket or wrench
  • Funnel
  • Distilled water (for optional flushing)
  • Gloves and eye protection
  • Shop rags

Preparation

  • Start with a completely cool engine to avoid burns from hot coolant or components.
  • Stabilize your dirt bike on a stand with the front wheel level or slightly elevated, helping air escape the cooling system.

Drain the Old Coolant

  • Remove the radiator cap. This relieves system pressure and allows thorough draining.
  • Locate the coolant drain bolt on the water pump cover (right side of the engine). On the 125SX, this is typically an 8mm bolt at the lowest point of the cover.
  • Place your drain pan underneath and remove the bolt. Allow all coolant to fully drain out.
  • Tip the bike gently from side to side to encourage full emptying, but avoid aggressive tilting to prevent any spills.

Optional: Flushing the Cooling System

  • If the old coolant is dirty or you suspect residue buildup, pour distilled water into the radiator, reinstall the drain bolt, run the engine briefly, then drain again. Repeat until water runs clear.

Refill with Fresh Coolant

  • Reinstall the drain bolt securely. Do not overtighten–a snug fit is enough to prevent stripping.
  • Slowly pour new coolant into the radiator until it reaches the fill neck. Gently rock the bike and squeeze the radiator hoses to help remove air bubbles.
  • On many KTM 125SX models, the left radiator is the fill point; always double-check before pouring.
  • Reinstall the radiator cap.

Burp the System

  • Start the engine and let it idle for several minutes. Keep an eye on the coolant level through the radiator neck (if accessible).
  • Turn off the engine, allow it to cool, and re-check the coolant level. Top off as needed to reach the lowermost part of the neck—never overfill.

Final Inspection and Notes

  • Check for leaks around the drain bolt and radiator cap after operating temperature is reached.
  • The 2009 KTM 125SX uses a relatively small cooling system, so always use the correct coolant type–avoid silicate-heavy formulas that might damage magnesium engine components.
  • If you ride in extremely cold conditions, verify your coolant's freeze point matches your local climate.
  • Routine coolant changes (at least annually, or after deep mud/sand rides) are best for longevity.

Following these steps will help ensure your 2009 KTM 125SX runs cool and reliably all season. Stay proactive with maintenance, and you will maximize the lifespan of your high-revving two-stroke engine.

Related Shopping Categories

Shop Radiators for a 2009 KTM 125SX Dirt Bike.

Shop Coolant for a 2009 KTM 125SX Dirt Bike.

Shop Temperature Sensors for a 2009 KTM 125SX Dirt Bike.

Shop Tools for a 2009 KTM 125SX Dirt Bike.

Shop Radiator Hoses for a 2009 KTM 125SX Dirt Bike.

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.