How to Change the Coolant on a 2020 KTM 125SX: A MotoSport Guide
Shop parts for a 2020 KTM 125SX Dirt Bike.
Keeping the cooling system on your 2020 KTM 125SX in top shape is essential for consistent power delivery and long engine life. Changing the coolant is a simple yet crucial maintenance task that you can confidently tackle in your own garage. This guide is crafted exclusively for MotoSport riders, focusing specifically on the unique features and requirements of the 2020 KTM 125SX.
What Makes the 2020 KTM 125SX Coolant System Unique?
The 2020 KTM 125SX is a high-revving two-stroke equipped with a robust radiator system designed for aggressive riding. Notably, this model uses a 1.2-liter (1.3-quart) coolant capacity, which is larger than some comparable bikes, ensuring optimal engine temperature during demanding rides. Also, radiator cap placement and the shape of the shrouds make accessing coolant components relatively straightforward for DIY maintenance.
Tools & Supplies Needed
- Fresh premixed coolant (ready-to-use, motorcycle-specific for aluminum engines)
- 8mm socket or wrench
- Drain pan or container
- Funnel
- Small torque wrench (for drain bolt reinstallation)
- Clean rag
- Safety gloves and eyewear
Step-by-Step Coolant Change Procedure
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Ensure the engine is cold.
Never open the radiator cap on a hot bike – there is pressurized hot coolant inside that can cause serious burns. -
Stabilize the bike upright.
Use a bike stand if possible. The 2020 KTM 125SX's frame and kickstand provide good stability for maintenance. -
Remove radiator shrouds if needed.
This may make accessing the cap and drain bolt easier, though some riders may be able to skip this depending on aftermarket plastics. -
Open the radiator cap.
Locate the cap on the left radiator (remove carefully). -
Locate and remove the coolant drain bolt.
The drain bolt is found at the bottom of the water pump cover on the right side of the engine. Place your drain pan underneath, use your 8mm wrench, and loosen the bolt to let old coolant drain completely out of the system. For best results, slightly rock the bike side-to-side to evacuate all fluid.
Inspect the copper crush washer; replace if damaged. -
Reinstall the drain bolt.
Once drained, wipe the area clean, reinstall the bolt, and torque to 15 Nm (11.1 lbf ft) for a proper seal. -
Refill the system.
Using a funnel, fill the radiator slowly to the very top with your premixed coolant. The system’s spec is 1.2L (1.3qt). Allow bubbles to escape for an accurate fill. -
Bleed trapped air.
Gently rock the bike and squeeze radiator hoses; watch for air bubbles rising at the filler neck. Fill again as needed until the coolant level stabilizes. - Reinstall radiator cap.
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Start the engine.
Let the bike idle until it’s warm. Shut down, allow it to cool briefly, and recheck the coolant level. Top off if required. -
Inspect for leaks.
Double-check the water pump bolt and all hoses for any sign of leakage after the engine warms up.
Pro Tips for 2020 KTM 125SX Owners:
- Only use coolants compatible with aluminum engines – silicate-free formulas protect gaskets and water pump seals unique to KTM hardware.
- If you ride in extreme heat or are racing, consider coolant with higher boiling points for improved performance consistency.
- Avoid overtightening the plastic radiator cap, as it can damage the seal or cap.
- Regular coolant checks prevent common overheating issues, a known trouble spot in aggressive riding or on tight motocross tracks.
With the right tools and knowledge, changing the coolant on your 2020 KTM 125SX is quick, straightforward, and keeps your power delivery at its best – on the trail, track, or anywhere you ride.
Related Shopping Categories
Shop Radiators for a 2020 KTM 125SX Dirt Bike.
Shop Coolant for a 2020 KTM 125SX Dirt Bike.
Shop Temperature Sensors for a 2020 KTM 125SX Dirt Bike.
Shop Tools for a 2020 KTM 125SX Dirt Bike.
Shop Radiator Hoses for a 2020 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.