How to Change the Coolant in a 2017 KTM 125SX: MotoSport Guide

Shop parts for a 2017 KTM 125SX Dirt Bike.

Keeping your 2017 KTM 125SX running cool and reliable is essential for performance on the track or trails. Changing the coolant is a critical piece of routine maintenance that's simple when you follow this step-by-step MotoSport guide. Here's how to change the coolant on your 125SX, plus a few specific pointers for this model year.

Preparation – What You Need

  • Fresh, motorcycle-approved coolant (refer to your owner's manual for specification)
  • 8mm socket or wrench
  • Basin or container for old coolant
  • Funnel (for clean filling)
  • Gloves and eye protection
  • Rags for clean-up

Step 1: Ensure a Cool Engine

Never attempt to open your radiator cap or drain coolant when the engine is hot. Allow the bike to cool completely to avoid burns or injury.

Step 2: Remove the Radiator Cap

With the engine cool, locate and slowly remove the radiator cap. It may have a safety catch – press down and turn gently to relieve any remaining pressure.

Step 3: Loosen and Remove the Coolant Drain Bolt

The 2017 KTM 125SX has a dedicated coolant drain bolt on the water pump cover, easily accessed on the left side of the engine. Use your 8mm socket to remove it over your drain pan. You may hear a slight air suction as fluid begins to drain.
Tip: Tilting the bike gently side to side can help drain every last bit of coolant.

Step 4: Inspect the Old Coolant

Check the color and clarity of your drained coolant. Extremely dirty, rusty, or oily fluid may be a sign of bigger issues – contact your mechanic if you spot anything unusual.

Step 5: Replace the Drain Bolt

Once drained, reinstall and gently tighten the drain bolt to factory specification. Avoid overtightening, as the threads in the water pump cover are easily damaged.

Step 6: Fill with Fresh Coolant

Using a funnel, slowly pour in fresh coolant through the radiator neck. Fill until the level just reaches the top of the cooling fins inside the radiator. On the KTM 125SX, avoid using automotive coolant with silicates or phosphates that can damage internal seals.

Step 7: Bleed Air from the System

With the radiator cap off, lean the bike side-to-side and gently squeeze radiator hoses to help release any trapped air. Once no more bubbles appear and the coolant level stays stable, secure the radiator cap back on.

Step 8: Warm Up and Recheck

Start the bike and let it idle for several minutes. Watch your coolant level through the radiator cap (if possible – if not, check after shutting the engine off and letting it cool). Add a small amount more if necessary, and check for leaks.

Model-Specific Notes: 2017 KTM 125SX

  • The 125SX uses an aluminum radiator without a catch tank. Periodic checks are essential, as vented coolant cannot be captured for return.
  • This model's cooling capacity is relatively small, so overheating from low coolant can quickly cause damage. Check the level frequently, especially before a long ride or race.
  • KTM recommends a non-silicate, non-phosphate coolant. Universal coolants are not advised for optimal corrosion protection.
  • Always rinse skin and eyes with plenty of water if exposed to coolant, and consult a doctor if ingested or in the eyes—this follows KTM safety guidance for owners.

This routine can be performed in under 30 minutes with a few basic tools. It's one of the simplest ways to extend your 2017 KTM 125SX's reliability & keep your race season worry-free.

Related Shopping Categories

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Shop Radiator Hoses for a 2017 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.