How to Change the Coolant in a 2024 KTM 125SX: Step-by-Step Guide

Shop parts for a 2024 KTM 125SX Dirt Bike.

Keeping your 2024 KTM 125SX running at peak performance means regularly maintaining the cooling system. Flushing and replacing the coolant is essential for engine protection and consistent power output, especially in high-revving 2-stroke machines like the 125SX. Follow this MotoSport proprietary guide crafted specifically for KTM's latest motocrosser to change your coolant safely and efficiently.

What You Need

  • Fresh, manufacturer-approved coolant (mixed, ready to use; 1.2 liters recommended)
  • 8mm and 10mm socket or wrench
  • Catch pan/container
  • Torque wrench
  • Funnel
  • Shop towels
  • Optional: New drain bolt washer

Preparation: Important Tips for the 2024 125SX

  • Always begin with a completely cool engine to avoid burns and ensure accurate coolant level checks.
  • Stand your KTM upright on level ground, using a stand if possible, for accurate draining and filling.
  • The 2024 KTM 125SX, like previous generations, uses a sealed cooling system. Take care when removing the radiator cap due to residual pressure.

Step 1: Remove the Radiator Cap

  • Ensure the engine is cold before starting.
  • Remove the seat and left radiator shroud if needed for easier access.
  • Slowly twist off the radiator cap (left radiator). If you hear hissing, pause and wait for pressure to release.

Step 2: Drain Old Coolant

  • Locate the coolant drain bolt. On the 125SX, this is typically found on the lower water pump cover on the right side of the engine–use a 10mm socket to loosen it–and position your catch pan beneath it–be ready, as coolant will flow quickly.
  • Completely remove the bolt to allow all coolant to drain out. For extra thoroughness, loosen the lower radiator hose if accessible to ensure full drainage.
  • Inspect the drain bolt washer and replace if worn to ensure a leak-free seal on reinstallation.

Step 3: Reinstall Drain Bolt

  • Clean the drain area and threads before reinstalling the bolt.
  • Tighten the drain bolt to 15 Nm (11.1 lbf ft) with a torque wrench for proper sealing.

Step 4: Refill with New Coolant

  • With the bike upright, insert a funnel into the radiator cap opening.
  • Pour in new coolant (1.2 liters recommended) until the fluid level sits just above the radiator fins.
  • Reinstall the radiator cap securely.

Step 5: Bleed and Check for Leaks

  • Start the engine and let it idle for several minutes until warm. This will help purge any trapped air out of the system.
  • Shut off the engine and allow it to cool, then carefully remove the radiator cap and top off coolant if needed.
  • Check all connections and the drain bolt for leaks.

2024 KTM 125SX Coolant System Notes

  • Factory Fill: KTM recommends using ethylene glycol-based, silicate-free coolant. Motorex M3.0 or comparable products are suitable. Always check owner's manual for precise specifications.
  • Capacity: The system holds roughly 1.2 liters–do not overfill.
  • Attention to Venting: Because modern KTM 2-strokes use high-flow water pumps and compact radiators, purge air pockets fully to avoid overheating risks.
  • Regular Inspection: Routinely inspect for leaking hoses or white residue, a sign of small leaks or previous boiling, both harmful to high-revving two-strokes.

When to Change Coolant on a KTM 125SX

  • Annually, at minimum, or every 40 hours of operation
  • Anytime coolant appears rusty, cloudy, or contaminated
  • After overheating or head gasket repair

Proper coolant maintenance on your 2024 KTM 125SX will keep the engine protected and performing at its best, session after session. For KTM-specific parts, tools, and coolant, MotoSport is your destination.

Related Shopping Categories

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Shop Temperature Sensors for a 2024 KTM 125SX Dirt Bike.

Shop Tools for a 2024 KTM 125SX Dirt Bike.

Shop Radiator Hoses for a 2024 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.