How to Change the Coolant in a 2019 KTM 125SX
Shop parts for a 2019 KTM 125SX Dirt Bike.
Maintaining optimal engine temperature is essential for your KTM 125SX's performance and longevity. The 2019 KTM 125SX uses a liquid cooling system that requires periodic coolant replacement for maximum efficiency and reliability. Below, MotoSport provides a proprietary, step-by-step guide tailored specifically for your model, including key tips unique to the 2019 125SX.
Why Change the Coolant?
Over time, coolant loses its protective properties, reducing its ability to manage heat and prevent corrosion inside your bike's radiator and engine components. Replacing your coolant at recommended intervals is vital – especially for a high-revving two-stroke like the 125SX, which naturally generates more heat and puts more demand on cooling than many four-strokes.
Tools & Supplies Needed
- Fresh, pre-mixed coolant (choose a formula compatible with aluminum components and local climate)
- Drain pan or container
- 8mm socket or wrench
- Torque wrench
- Shop towels or rags
- Funnel (optional, for easy pouring)
- Protective gloves and eyewear
Important Note for the 2019 KTM 125SX Owner
This model features a lightweight aluminum radiator and water pump that require careful handling. Over-tightening the drain bolt or suspect coolant selection can damage the system. Always use a torque wrench, and never fill with straight water – proper antifreeze mix is required for both corrosion protection and boiling point elevation.
Step-by-Step Coolant Change Guide
- Let the engine cool. Never attempt to open the radiator cap on a hot engine. Wait until everything is completely cool to the touch.
- Position the bike upright. Place your 125SX on a flat, stable surface using a bike stand for best access.
- Access the radiator cap. Remove the seat and plastics if necessary for unimpeded access. Open the radiator cap slowly to relieve any lingering pressure.
- Locate the drain bolt. The KTM 125SX's coolant drain bolt is situated on the water pump cover, typically on the right side of the engine. Use an 8mm wrench or socket to remove it, and allow coolant to flow into your drain pan–expect some splash and occasional stubborn flow as air enters the system–this is normal.
- Remove the coolant completely. Tip the bike gently side-to-side to facilitate full drainage. Inspect the coolant for excessive debris or oil, which can indicate mechanical issues.
- Reinstall the drain bolt. Inspect and clean the bolt threads. Refit the drain bolt with a fresh seal ring if necessary and torque to 15 Nm (11.1 lbf ft) to prevent leaks and avoid stripping the threads.
- Fill with new coolant. Using a funnel, slowly add pre-mixed coolant to the radiator until full. The 2019 KTM 125SX has a capacity of approximately 1.2 liters (1.3 quarts). Air pockets in the system can cause overheating, so take your time pouring.
- Bleed the system. Briefly loosen the radiator's bleed screw if equipped (often found at the highest point). Tighten once coolant appears without bubbles.
- Replace the radiator cap. Ensure the cap is secured tightly with its rubber seal in good condition.
- Warm up the engine. Start the motor and let it idle with the radiator cap on. After a few minutes, shut the engine off, let it cool, and re-check the coolant level – top off as needed.
Additional Tips
- Dispose of old coolant responsibly. Used coolant is hazardous to the environment and animals.
- Inspect radiator hoses and clamps for wear or cracks while the coolant is drained. Replace as needed to avoid leaks mid-ride.
- Check the water pump housing for corrosion – a sign incompatible or expired coolant was used previously.
- Flush with distilled water if the old coolant was especially dirty, repeating the drain/fill steps before adding fresh coolant.
Keeping your 2019 KTM 125SX's cooling system fresh ensures peak power throughout your moto season and helps guard against costly engine repairs. For genuine replacement parts, premium coolants, and essential tools, choose MotoSport for fast shipping and expert support.
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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.