How to Change the Coolant in a 2023 KTM 125XC: Step-by-Step Guide

Shop parts for a 2023 KTM 125XC Dirt Bike.

Changing your coolant is a vital part of routine maintenance for the 2023 KTM 125XC. Proper coolant replacement helps the advanced two-stroke engine maintain optimal temperature, avoids overheating, and ensures maximum engine longevity. Read below for a step-by-step process designed specifically for the KTM 125XC, along with tips every owner should know about their model’s cooling system.

What You’ll Need

  • Coolant recommended for aluminum motorcycle radiators (pre-mixed, NOT just water-based antifreeze)
  • Catching pan or bucket (min. 1.5 liters capacity)
  • 8mm socket or wrench
  • Funnel
  • Torque wrench (recommended)
  • Gloves – engine coolant can irritate skin
  • Rags for cleanup

Step 1: Prepare Your Bike

  • Make sure the engine is completely cool before starting. Hot coolant is dangerous and may cause burns.
  • Stand the bike upright on a level surface or bike stand. This helps you to access the drain bolt and ensures a full drain and refill.

Step 2: Remove the Radiator Cap

  • Remove the left side shroud if easier access is needed.
  • Find the radiator cap on the left top side of the radiator. To relieve system pressure, press down and rotate the cap counterclockwise.

Step 3: Drain the Old Coolant

  • Locate the coolant drain bolt on the lower part of the water pump (right side of the engine near the clutch cover). This bolt is usually 8mm.
  • Place your drain pan beneath and carefully loosen the bolt. Coolant will begin to flow out.
  • Allow fluid to drain completely—tilting the motorcycle slightly side-to-side can help remove trapped fluid.
  • Inspect the old coolant for unusual debris, which may indicate internal engine issues.

Step 4: Reinstall the Drain Bolt

  • Clean the bolt and sealing surface. If your manual specifies, replace the washer or seal for a sure fit.
  • Reinstall the drain bolt and torque to KTM spec: 15 Nm (11.1 lbf ft) for typical KTM small-displacement models*.

Step 5: Refill with New Coolant

  • Using a funnel, pour new coolant into the radiator until full. The 2023 KTM 125XC radiator capacity is approximately 1.2 liters (1.3 quarts)*.
  • Replace the radiator cap.

Step 6: Bleed the Cooling System

  • Start the engine and let it idle for several minutes with the radiator cap on.
  • Watch the temperature gauge and check for leaks around the drain bolt.
  • Shut off the engine and allow it to cool, then check coolant level again. Top off if necessary.

KTM 125XC Technical Notes

  • The 2023 125XC uses KTM’s advanced WP radiators, which are highly efficient but have precise fill requirements—do not overfill.
  • Always use a coolant compatible with magnesium and aluminum. KTM does not recommend pure water or automotive coolants containing silicates or phosphates, as these can cause corrosion in dirt bike engines.
  • Check the radiator cap for a good seal. A leaking cap can lower cooling efficiency and trigger overheating.
  • If you operate your 125XC in hot climates or extended motos, inspect your coolant level more frequently—the XC is a cross-country race bike designed for aggressive riding.

*Capacity and torque guidelines are based on manufacturer specs for KTM small-displacement two-stroke models; consult your model tag or owner manual if in doubt.

Related Shopping Categories

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Shop Radiator Hoses for a 2023 KTM 125XC 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.