How to Change the Coolant on a 2020 Honda CRF125FB

Shop parts for a 2020 Honda CRF125FB Dirt Bike.

Changing the coolant on your 2020 Honda CRF125FB keeps your engine running cool – and protects it from corrosion. This model, part of Honda's air-cooled trail bike family, is known for its reliability but still demands timely maintenance to perform its best. Follow this MotoSport.com guide for a straightforward, model-specific coolant flush and refill.

What You Need

  • Fresh silicate-free motorcycle coolant (pre-mixed 50/50 recommended)
  • Clean funnel
  • 8mm, 10mm sockets and ratchet
  • Phillips screwdriver
  • Drain pan
  • Rags or paper towels
  • Safety gloves and eye protection

Preparation

  • Make sure the bike is on a level surface and the engine is completely cool.
  • Engage the bike's stand for stability during maintenance.

Step 1: Remove Body Panels for Access

  • Remove the left side cover by taking out the necessary bolts and gently disengaging the cover from its grommets and tabs. (The owner's manual provides bolt locations – pay attention to panel fitment during re-installation for a secure fit.)
  • If needed, remove the seat or other nearby plastic panels to reveal the radiator and fill area.

Step 2: Drain the Old Coolant

  • Position a drain pan beneath the water pump and radiator area.
  • Locate the coolant drain bolt at the base of the water pump.
  • Slowly loosen and remove the drain bolt, then allow coolant to fully drain. Open the radiator cap to speed draining and prevent vacuum lock.
  • Dispose of old coolant responsibly – do not pour into drains or on the ground.

Step 3: Flush the System (Optional but Recommended)

  • If the coolant was dirty or you're unsure of its history, flush the radiator by pouring distilled water into the fill neck, letting it drain fully before adding new coolant.

Step 4: Reinstall the Drain Bolt

  • Inspect the drain bolt washer. Replace it if damaged or crushed. Reinstall the drain bolt and tighten securely – but do not overtighten to avoid stripping the threads.

Step 5: Add New Coolant

  • Using a clean funnel, pour fresh coolant into the radiator fill neck until it reaches the correct level.
  • On the CRF125FB, check the overflow reservoir and add coolant to the proper line if needed.

Step 6: Bleed Air from the System

  • With the radiator cap still off, start the engine and let it idle for several minutes. Watch for air bubbles to surface; add more coolant as needed.
  • When bubbles stop, the coolant level stabilizes, and the engine warms up, turn off the bike and let it cool.
  • Check and top off radiator and reservoir levels before sealing the radiator cap.

Step 7: Reassemble and Inspect

  • Reinstall the left side cover and any other panels you removed. Make sure all bolts and grommets are properly secured.
  • Wipe up any spilled coolant and start the engine again, checking for leaks or drips around the drain bolt, hoses, and radiator cap.
  • After a short ride, recheck coolant levels and inspect for leaks.

Important Model-Specific Notes

  • The 2020 CRF125FB is an air-cooled model, so it doesn't have a radiator like Honda's liquid-cooled CRFs. Instead, maintenance focuses on maintaining airflow, cooling fins, and ensuring proper oil change intervals. However, there is a coolant circuit for the starter-motor-driven, small auxiliary cooling system. If you're unsure about cooling system components, consult your owner's manual before beginning.
  • Always use Honda-approved coolant or a high-quality equivalent to prevent corrosion or gasket damage.
  • If your CRF125FB is ridden in particularly harsh or muddy conditions, inspect for clogged cooling fins and debris buildup after coolant service.

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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.