How to Change the Coolant in a 2018 Honda CRF125F: MotoSport's Expert Guide

Shop parts for a 2018 Honda CRF125F Dirt Bike.

Fresh coolant is critical to keep your 2018 Honda CRF125F's engine running at proper temperatures – preventing overheating, performance drops, and costly repairs. Whether you're chasing trails or prepping for storage, a coolant change should be part of your regular maintenance, typically every two years or after 40–50 hours of ride time, whichever comes first. Here's MotoSport's proprietary guide to changing coolant specifically for this model.

What You'll Need

  • Silicate-free 50/50 premixed coolant (recommended: motorcycle-specific)
  • Drain pan
  • 10mm socket and ratchet
  • Phillips screwdriver
  • Funnel
  • Fresh copper or aluminum crush washer (for drain bolt, optional but recommended)
  • Shop towels
  • Safety gloves & eyewear

Step 1: Prepare Your CRF125F

  • Let the engine cool completely before starting – opening the radiator cap on a hot bike can cause dangerous burns from hot coolant or steam.
  • Prop the bike on a stable stand.

Step 2: Remove Side Covers

  • To access the radiator cap and the reservoir, remove the left side cover. Remove Bolt A and Bolt B, plus the collar, then pull out the prong and boss as described in your owner's manual. Keep hardware secure for reassembly.
    Note: The CRF125F's side covers are designed for quick removal to simplify essential maintenance, a benefit for trail-side repairs or routine upkeep.

Step 3: Remove Radiator Cap

  • Locate the radiator cap on the left side of the bike, behind the side cover.
  • Remove the securing screw if present, then twist off the radiator cap.
  • Never remove the cap if the engine is still hot.

Step 4: Drain the Old Coolant

  • Place your drain pan underneath the water pump – on the right side of the engine, you'll find the coolant drain bolt (typically with a copper washer).
  • Use the 10mm socket to carefully remove the drain bolt.
  • Allow all coolant to drain out completely.
    Tip: Rock the bike gently to ensure full drainage. For a thorough flush, you can add a bit of distilled water and let it drain out as well.

Step 5: Reinstall Drain Bolt

  • If you have a new crush washer, install it now to ensure a tight seal and prevent leaks.
  • Tighten the drain bolt securely, but do not overtighten to avoid damaging the threads.

Step 6: Fill with Fresh Coolant

  • Insert a funnel and pour in the new coolant up to the base of the radiator neck.
  • If your CRF125F has a reservoir bottle, top it off to the "full" mark as well.

Step 7: Burp the Cooling System

  • With the cap off, start the engine and let it idle for 1–2 minutes.
  • Watch for air bubbles escaping from the radiator neck – this allows trapped air to escape for a proper fill.
  • Shut off the engine, let it cool slightly, and check the coolant level. Top off if needed.

Step 8: Reassemble the Bike

  • Reinstall the radiator cap and secure it with its screw if needed.
  • Reattach the left side cover, making sure all bolts, tabs, and grommets are secured as designed for the CRF125F platform.

Step 9: Final Check

  • Inspect for leaks around the drain bolt and cap area.
  • After your next short ride, recheck the coolant level and top off if necessary.

MotoSport Pro Tips for Your 2018 CRF125F

  • Coolant selection matters: Always use a silicate-free coolant designed for aluminum radiators. Avoid automotive coolants with silicates or phosphates, as these can damage internal passageways and seals.
  • Model-specific access: The CRF125F has easy-to-remove side covers for fast service. Follow the owner manual's diagram to avoid breaking tabs or losing hardware during coolant changes or other common maintenance.
  • Overflow routing: Like other CRF models, the overflow tube routes below the frame – a little overfill may vent harmlessly to the ground. Routinely check for split hoses or blockages, especially after aggressive riding.
  • Routine inspection: Honda's recommended intervals help prevent corrosion, overheating, and premature water pump or gasket wear – especially if you ride in muddy or sandy conditions.
  • Safe disposal: Used coolant is toxic – always dispose of it according to your local regulations.

Changing your coolant is simple, but it's one of the best ways to keep your 2018 Honda CRF125F running cool and strong for seasons of rides. If you find yourself needing replacement hoses, radiators, or even simple hardware during your next service, MotoSport has you covered with OEM-quality parts and upgrades for your model year.

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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.