How to Change the Coolant in a 2011 KTM 150SX: A MotoSport.com Guide

Shop parts for a 2011 KTM 150SX Dirt Bike.

Keeping your KTM 150SX running cool is essential for peak performance and engine longevity. Changing the coolant regularly is a straightforward task, but a few steps are unique to this high-strung two-stroke. Follow this MotoSport.com guide to service your 2011 KTM 150SX – a favorite in the motocross world for its potent power delivery and lightweight chassis.

What You Need

  • New coolant (aluminum-safe and silicate-free; check for minimum -25C/-13F protection as recommended for KTM bikes)
  • Drain pan or suitable catch container
  • 8mm socket or wrench
  • Funnel
  • Clean shop towel or rag
  • Torx tools if applicable to body panel removal
  • Safety gear: gloves and eye protection

Preparation

  • Ensure the bike is completely cool to avoid burns or injury.
  • Place the bike on a stable stand in a well-ventilated area.
  • Remove the right side radiator shroud if access is limited.

Draining the Old Coolant

  1. Remove the radiator cap to relieve pressure and allow air in for a better drain.
  2. Locate the water pump drain bolt – typically on the lower right side of the engine (use the 8mm wrench).
  3. Position the drain pan under the bike. Slowly loosen and remove the drain bolt. Allow all coolant to drain completely.
  4. You may want to slightly rock the bike side to side or remove the lower radiator hose for extra drainage, but this is generally not necessary unless doing a full flush.

Flushing (Optional but Recommended)

  • If the coolant was particularly dirty or contaminated, fill the system with distilled water, replace the drain bolt, run the engine briefly, then drain again.

Refilling with Fresh Coolant

  1. Reinstall the drain bolt securely, ensuring the sealing washer is in good condition. Do not overtighten.
  2. Using a funnel, slowly fill the radiators with your new coolant until you reach the fill line or just below the bottom of the neck on the filler opening.
  3. Tip for the 150SX: Gently tilt or lift the front of the bike (a helper can hold it about 20-50 cm higher) while filling to encourage air bubbles to escape from the cylinder head & radiators.
  4. Briefly squeeze the upper radiator hose by hand to help burp out any trapped air.
  5. Top off coolant as the level drops. When full, reinstall the radiator cap securely.

Start & Check

  • Start the engine and let it warm up at idle for a minute or two – do not rev the engine on a cold start.
  • Shut off the engine and allow it to cool. Remove the cap cautiously, and check the coolant level again. Top off if needed.

2011 150SX-Specific Notes

  • Radiator fins are prone to damage from mud and debris in racing. Gently straighten bent fins with a thin flat instrument and always keep them clean for optimal airflow.
  • If riding in sand or muddy conditions, check and clean your cooling system and air filter more frequently.
  • This model uses a high-compression 2-stroke engine – keep an eye on temp fluctuations as clogged cooling or low coolant levels can cause rapid overheating.
  • KTM recommends checking the carburetor setting for different conditions, as improper tuning can affect engine temps and coolant life.

Disposal

  • Never dispose of used coolant down the drain or on the ground. Always take it to a certified recycling or hazardous waste facility.

Routine coolant changes not only protect your KTM 150SX engine—they also help you spot small issues before they become big problems. Following the above steps helps ensure your bike runs cool and strong, season after season.

Related Shopping Categories

Shop Radiators for a 2011 KTM 150SX Dirt Bike.

Shop Coolant for a 2011 KTM 150SX Dirt Bike.

Shop Temperature Sensors for a 2011 KTM 150SX Dirt Bike.

Shop Tools for a 2011 KTM 150SX Dirt Bike.

Shop Radiator Hoses for a 2011 KTM 150SX 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.