How to Change the Coolant in a 2010 KTM 105SX

Shop parts for a 2010 KTM 105SX Dirt Bike.

Regular coolant changes are crucial for your 2010 KTM 105SX – maintaining optimal engine temperatures and preventing internal damage. The KTM 105SX uses a high-performance, two-stroke engine that can generate extra heat, especially under motocross conditions, so periodic coolant service is vital to engine longevity and race-day reliability.

What You Need

  • Phillips screwdriver or socket set
  • Catcher pan
  • Fresh coolant (KTM recommends high-quality, 50/50 pre-mix)
  • Distilled water (optional, if flushing)
  • Protective gloves and eyewear
  • Shop rags

Coolant Change Procedure

  1. Let the bike cool down completely. Coolant is under pressure when hot–removing the cap could cause a dangerous spray. Only proceed when the engine is cold.
  2. Access the radiators. Remove the seat and shrouds if they obstruct access to the radiator cap or right-side radiator.
  3. Position a drain pan beneath the right side of the engine to catch old coolant.
  4. Remove the radiator cap. Next, find the drain bolt on the right-side radiator or at the base of the water pump with your tools and carefully loosen it. Allow all coolant to drain fully. If needed, carefully wiggle the bike to help empty out all liquid.
  5. Inspect and flush (optional). If the coolant is especially dirty, pour distilled water through the system until it runs clear, then let the bike drain completely again.
  6. Reinstall the drain bolt and ensure it is tight, then prepare to refill.
  7. Begin refilling:
    • Pour approximately 0.5 liters of new coolant into the left radiator.
    • Loosen the bleed bolt located on the right radiator.
    • Add coolant slowly until it emerges free of air bubbles at the bleed bolt. Immediately retighten the bolt to prevent air from entering.
    • Continue filling the main (left) radiator until coolant sits about 10 mm above the cooling fins. The total capacity is about 1 liter for the KTM 105SX*.
  8. Purge air: Air pockets in the two-stroke KTM cooling system can cause severe overheating. To fully purge:
    • ELEVATE the front wheel if possible to help trapped air escape from the cylinder area.
    • After filling, briefly start the engine and let it idle with the radiator cap off (watch fluid level and avoid spillover).
    • Turn off the bike and top up coolant as needed.
  9. Reinstall the radiator cap and bodywork.
  10. Check for leaks. After running the bike and a short, gentle ride, inspect for any leaks around hoses and radiators. Double-check fluid level once the bike cools down again, as extra air may escape during the first heat cycle.

Important Notes for 2010 KTM 105SX Owners

  • KTM Cooling System: This model's compact radiators and high-revving engine make it sensitive to even small air pockets. Always thoroughly bleed air when refilling.
  • Chemical compatibility: Use only silicate-free, motorcycle-specific coolant to protect the internal magnesium parts and seals.
  • Throttle cable check: After major maintenance, ensure 3-5 mm of play in the throttle cable. An improper throttle cable setting can cause inconsistent idling or engine runaway.
  • Cooling capacity: For this model, the total coolant capacity is about 1 liter. Do not overfill–excess coolant can be expelled and create a mess in the catch tank.

Final Considerations

Always dispose of old coolant responsibly, as it is toxic to people and animals. Routine inspection and cooling system service give you confidence on the track and help keep your KTM 105SX running at its best. If you ever have doubts about the process, your MotoSport support team is here to help.

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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.