How to Change the Coolant in a 1986 Honda CR125

Shop parts for a 1986 Honda CR125 Dirt Bike.

Proper cooling system maintenance is vital to keep your 1986 Honda CR125 running crisp and strong through every lap. This guide from MotoSport walks you through every step needed to drain, flush, and refill your coolant – with expert-level tips specific to your classic CR125.

Tools & Supplies You'll Need

  • Clean drain pan
  • Distilled water
  • New coolant (dedicated motorcycle or race-approved formula is best)
  • 8mm & 12mm sockets/wrenches
  • Pliers for hose clamps
  • Compressed air nozzle (optional for full system flush)
  • Funnel
  • Shop towels

Steps to Change the Coolant

  1. Let your CR125 cool completely.
    Never open a hot radiator – wait until everything is cool to the touch to avoid burns or injury.
  2. Remove the seat and fuel tank.
    This opens full access to the radiator and associated hoses, making it easier and cleaner to work on the system.
  3. Position a drain pan beneath the water pump area.
    Locate the drain bolt (usually at the base of the water pump on the right side of the engine). Loosen and remove the bolt, allowing old coolant to drain completely.
  4. Disconnect the lower radiator hose.
    Using pliers, remove the clamp at the lowest point and pull the hose free. Wiggle gently if needed; some residual coolant may spill out, so keep the pan ready.
  5. Flush the system (recommended).
    With the drain bolt and lower hose still off, fill the radiator with distilled water. Let it drain, then repeat until the water runs clear. For a thorough flush, use compressed air to blow out remaining water and debris via the radiator cap opening and hoses.
  6. Reattach all hoses and the drain bolt.
    Inspect all hose clamps and seals – replace any that are worn or cracked before torquing everything back to spec.
  7. Refill with fresh coolant.
    Through the radiator filler neck, slowly pour in your recommended premixed coolant until the radiator is full. Avoid using straight tap water, as minerals may leave deposits in your passages.
  8. Bleed the system of air.
    Gently rock or tap the bike side to side. With the cap off, kick the engine over several times (with kill switch held or plug disconnected) to let air bubbles escape. Top off as necessary.
  9. Reinstall the radiator cap, tank, and seat.
  10. Warm up the engine and check levels.
    Let the bike idle until warm, then shut off and let cool. Recheck coolant; top off if needed.

CR125 Model-Specific Tips

  • Check the radiator cap and gaskets.
    Leaks or pressure loss are common on older bikes – inspect the cap and all junctions when you perform a coolant change.
  • Inspect power valve cover and water pump seals.
    Failures in these areas are a known issue on vintage CRs; seepage here may cause pressure loss or contamination. Address any suspicious moisture or leakage before you ride hard.
  • Coolant type matters for racing.
    If you race, note that some tracks ban regular antifreeze. Use distilled water with a race-safe additive if required. For trail use, a high-quality motorcycle coolant with corrosion inhibitors is recommended.

Final Safety Checks

  • Always check the coolant level after your initial ride – air pockets sometimes work out of the system and could leave you low.
  • Inspect for leaks around all connections with the engine warm and running.
  • Never overfill the radiator; leave slight room for coolant expansion.

Changing your coolant is a quick, high-impact way to extend the life of your 1986 Honda CR125. Your cooling system will thank you with every lap.

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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.