How to Change the Coolant in a 2015 KTM 125SX
Shop parts for a 2015 KTM 125SX Dirt Bike.
Regular coolant changes are key to the longevity and peak performance of your 2015 KTM 125SX. This 2-stroke race bike features a liquid-cooled engine, making its coolant system crucial for proper engine temperatures and preventing overheating. Below, MotoSport.com guides you through this procedure safely and efficiently, with details specific to your model.
What You Need
- Fresh coolant compatible with KTM 2-stroke models
- Drain pan or container
- 8 mm socket or wrench
- Shop rags and gloves
- Funnel (recommended)
- Distilled water (for optional flushing)
Drain the Old Coolant
- Ensure the engine is completely cool to avoid burns.
- Remove both radiator shrouds for easier access to the radiator cap and drain plug.
- Put your drain pan beneath the water pump at the lower right side of the engine.
- Twist the radiator cap open to release pressure.
- Locate and loosen the coolant drain bolt on the water pump cover with your 8 mm socket. Let all old coolant drain completely.–For all KTM 125SX years, the drain bolt location is consistent–look just below the water pump casing.–
- Inspect the old coolant for debris or discoloration, which can point to deeper engine issues.
Flush the System (Optional)
- If you see significant debris or you are switching coolant types, pour distilled water through the radiator, let it drain, and repeat until clear.
- Close the drain bolt and tighten to OEM torque (typically about 6 Nm).
Add New Coolant
- With the drain bolt secure, insert a funnel into the radiator neck.
- Slowly pour the fresh coolant into the radiator. The 2015 KTM 125SX takes about 0.65 liter; fill until coolant just reaches the lip inside the radiator.
- Tip: Elevating the front wheel about 19 inches can reduce air pockets during refilling on some KTMs–.
- Reinstall the radiator cap, making sure it's seated tightly.
Bleed Air from the System
- Start the engine and let it idle briefly, allowing coolant to circulate and air to move upward.
- Shut off after 1–2 minutes. Carefully loosen and retighten the radiator cap to check/restore the coolant level. Top off if necessary.
- Check for leaks at the drain bolt and hose connections.
Model-Specific Tips for the 2015 KTM 125SX
- Monitor coolant level regularly—overfilling or underfilling can affect performance.
- The KTM's 2-stroke design runs hotter under competitive conditions, so always use high-quality, motorcycle-specific coolant.
- The water pump shaft and seal are known wear points—inspect the area around the drain bolt and water pump cover for any residue or weeping each time you service coolant.
Final Checks
- Replace the radiator shrouds and wipe down any spilled coolant.
- Safely dispose of the old coolant according to local environmental regulations.
- Before your first ride after a coolant change, double-check the coolant level once the bike has cooled down again after running briefly.
Whether racing or trail-riding, keeping the cooling system of your 2015 KTM 125SX maintained ensures reliable, consistent performance. For more parts, accessories, and maintenance gear, MotoSport.com is your source for everything dirt bike.
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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.