How to Change the Coolant in a 2013 KTM 125SX: A MotoSport Guide

Shop parts for a 2013 KTM 125SX Dirt Bike.

Changing the coolant in your 2013 KTM 125SX is an essential maintenance step to keep your two-stroke performing at its peak and protect your engine from overheating and corrosion. Follow this exclusive MotoSport guide for a safe, effective coolant change tailored specifically for the KTM 125SX–with tips noted for this legendary model.

What You Need

  • Fresh, manufacturer-approved coolant (ethylene glycol-based, silicate-free)
  • Catch pan for old coolant
  • 8mm wrench or socket (for the drain bolt)
  • Funnel
  • Distilled water (optional, for system flush)
  • Shop towels
  • Protective gloves

Preparation

  • Make sure the engine is completely cool to avoid burns from hot coolant or pressurized systems.
  • Stand your bike upright to ensure thorough draining.

Drain the Old Coolant

  1. Remove the radiator cap. If your 125SX has a safety latch, press down and twist counterclockwise.
  2. Locate the coolant drain bolt on the water pump (right side, at the base of the engine). Use your 8mm wrench to remove this bolt, and position your catch pan below to collect all old coolant.
    Note: KTM 125SX models from 2004–2013 share nearly identical drainage systems. Be sure to replace or inspect the copper washer under the drain bolt if needed.
  3. Allow coolant to fully empty. For a thorough job, you may also remove the lower radiator hose briefly to expel any trapped fluid. Reinstall the drain bolt securely once draining is complete.

(Optional) Flushing the Cooling System

  • If your coolant was badly contaminated or you're making a full switch (e.g., to a race-specific additive), pour distilled water into the radiator, reinstall the cap, run the engine for a minute, then drain as above.

Refill with Fresh Coolant

  1. Slowly pour new coolant into the radiator using a funnel, stopping periodically to let air bubbles escape.
  2. To help vent trapped air, briefly loosen (but do not remove) the small bleed screw on top of the cylinder head until coolant flows out, then retighten. Tilting the bike slightly to the right can assist.
  3. Fill until coolant level is just below the filler neck when the bike is vertical.
  4. Reinstall the radiator cap.
  5. If your 125SX has an auxiliary coolant recovery/overflow tank, fill to the MAX line.

Inspection & Bleeding Tips for the 2013 KTM 125SX

  • Never use plain water as a long-term coolant. Ethylene glycol-base, silicate-free coolants are required to prevent corrosion and overheating common in 2-stroke KTM engines.
  • Start the motorcycle and let it idle for a few minutes with the radiator cap closed to circulate coolant and purge any trapped air.
  • Shut off, let the engine cool, then recheck the coolant level and top off if needed. Repeat this process once to ensure no airlocks remain.

Special Notes for 2013 KTM 125SX Owners

  • This generation uses a high-revving 2-stroke engine with a relatively small cooling system, making regular coolant changes more critical than on four-strokes.
  • Inspect hoses, the radiator core, and the water pump for leaks or cracks—a common issue if the bike is ridden hard or stored in freezing temps.
  • Always use manufacturer-specified coolant volumes and maintain the correct blend to avoid overheating or premature wear.
  • Monitor coolant color; contamination can indicate a failing gasket or internal corrosion, which should be addressed immediately.

By following these steps, you can ensure your 2013 KTM 125SX continues to deliver legendary performance on every moto. For OEM and aftermarket coolant, radiators, hoses, or replacement water pump parts, explore MotoSport's selection and always ride prepared.

Related Shopping Categories

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Shop Radiator Hoses for a 2013 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.