How to Change the Coolant in a 2021 KTM 350EXCF: Step-by-Step Maintenance Guide

Shop parts for a 2021 KTM 350EXCF Dirt Bike.

Keeping your 2021 KTM 350EXCF running cool is essential for consistent performance on the trail. Coolant replacement is a simple but critical maintenance task, especially if you ride in demanding conditions or notice your engine's fan running frequently. Here's MotoSport's proprietary guide to changing the coolant in your KTM 350EXCF, with key model-specific tips for KTM enthusiasts.

What You'll Need

  • Fresh, compatible coolant (silicate-free, motorcycle-specific)
  • Distilled water
  • 8mm socket or wrench
  • Catching container – for old coolant
  • Funnel (optional, but highly recommended)
  • Torque wrench (optional, for reinstalling the drain bolt)
  • Gloves & rags for cleanup

Drain the Old Coolant

  1. Ensure the engine is completely cool to safely avoid scalding.
  2. Remove the seat and plastics as needed for clear access to the radiator cap.
  3. Place the catching container beneath the water pump (typically right-hand side of the engine).
  4. Remove the radiator cap to break the vacuum and allow the system to drain freely.
  5. Locate the coolant drain bolt at the bottom of the water pump. This should be an 8mm bolt.
  6. Carefully remove the drain bolt. Allow all coolant to drain.
  7. Inspect the drained fluid. Any oil, sludge, or foreign debris may signal other issues requiring inspection.

Flush the System (Highly Recommended)

  1. Reinstall the drain bolt (hand-tight), then fill the radiator with distilled water.
  2. With the radiator cap off, start the engine (outside, in a well-ventilated space), and run for 3-5 minutes to circulate the rinse water.
  3. Turn engine off, let it cool, then repeat the draining process.
  4. Repeat this flush step if the rinse water is still dirty.

Add New Coolant

  1. Reinstall the drain bolt securely. Tighten to factory spec (consult manual for exact torque).
  2. Fill the radiator slowly with fresh coolant until full. Some air will remain in the system – address this in the next step.
  3. On KTM 350EXCF models, you may need to elevate the front wheel (about 19 inches) to ensure all air bubbles rise to the top, especially after radiator service or a full flush.
  4. Start the engine briefly with the radiator cap off, letting the coolant circulate and allowing air to escape. As bubbles emerge and coolant level drops, top off as needed. Shut down the engine if coolant approaches the cap's opening.
  5. Check for any leaks around the drain bolt and hoses.
  6. Replace the radiator cap securely.

Bleeding, Checking, and Topping Off

  • After running the bike through a full heat and cool cycle, re-check coolant level.
  • If your 350EXCF has cylinder head bleed screws (consult your manual), open these briefly while filling to ensure no air pockets are trapped in the cylinder head.
  • Check the overflow/tank level (if fitted) and top off as necessary with the same coolant.

Model-Specific Tips for the 2021 KTM 350EXCF

  • This model's water pump drain bolt is easily accessible on the right side; make sure you don't strip the threads or overtighten during reassembly.
  • Avoid mixing coolant types. Use a high-quality, silicate-free motorcycle coolant only—never standard automotive antifreeze.
  • The KTM cooling system is sensitive to air pockets. Always take extra time bleeding air, especially after full flushes or repairs.
  • If your KTM is equipped with an electric fan, a properly filled and bled cooling system will reduce unnecessary fan cycling and prevent overheating in technical terrain.

Dispose of Old Coolant Properly

  • Never pour used coolant down a drain or onto the ground. Take it to a local recycling or hazardous waste facility.

Maintaining the coolant system on your 350EXCF keeps you riding longer and harder. Shop parts for your ride now and be ready for every trail or race.

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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.