How to Change the Coolant in a 1991 Honda CR125

Shop parts for a 1991 Honda CR125 Dirt Bike.

Routine coolant changes keep your 1991 Honda CR125 running at optimal temperature, prevent overheating, and reduce internal corrosion. This iconic two-stroke dirt bike features a liquid-cooled system that's easy to service but requires close attention to avoid air bubbles and ensure proper filling. Follow this step-by-step guide developed specifically for MotoSport riders.

Tools – Supplies Needed

  • Philips or flathead screwdriver
  • Metric socket set (8mm, 10mm)
  • Clean drain pan
  • Fresh coolant (Honda type or high-performance motocross coolant)
  • Distilled water (if flushing)
  • Shop towels
  • Funnel

Step 1: Preparation

  • Allow the engine to cool completely before servicing to avoid burns.
  • Place the bike on a stable stand with both wheels off the ground for easy access.
  • Turn the fuel valve OFF and, if desired, remove the seat and side panels for better access to the radiators.

Step 2: Draining Old Coolant

  • Remove the radiator cap slowly to relieve system pressure.
  • Locate the coolant drain bolt on the lower water pump cover (right engine case). Position the drain pan below the bolt.
  • Loosen the drain bolt with your 8mm or 10mm socket. Allow coolant to fully drain. To speed the process, gently tilt the bike side-to-side.
  • Inspect the drain bolt and crush washerreplace the washer if damaged to prevent leaks.

Step 3: Flushing the System (Optional but Recommended)

  • Reinstall the drain bolt temporarily. Pour distilled water into the radiator filler neck until full.
  • Replace the radiator cap. Start the engine and run it for 2–3 minutes to circulate the water, then shut off the engine.
  • Repeat the drain procedure to remove the flush water and any remaining sediment from the system.

Step 4: Filling with Coolant

  • Reinstall and tighten the drain bolt with the crush washer.
  • Using a funnel, slowly pour fresh coolant into the left radiator until full.
  • Gently rock the bike side-to-side and squeeze the radiator hoses by hand to help air bubbles escape.
  • Top off the coolant if the level drops.
  • Install the radiator cap securely.

Step 5: Burping and Final Check

  • Start the engine and let it idle for a few minutes. This circulates coolant and purges trapped air.
  • Shut off the engine. Let the bike cool, then recheck coolant level via the cap. Top off if needed.
  • Inspect the systemhose connections, drain bolt, and radiator capfor any leaks.

What Every 1991 Honda CR125 Owner Should Know

  • System Capacity: The 1991 CR125's smaller radiators and high-revving two-stroke nature require high-quality, motocross-specific coolant to prevent overheating during hard riding.
  • Crush Washer: Always inspect and replace the drain bolt's crush washer if worn or deformed to protect against leaks.
  • Air Bubbles: This model is especially prone to trapped air pocketsalways burp the system thoroughly to maintain cooling efficiency.
  • Coolant Change Interval: Honda recommends replacing coolant every two years or more frequently in race or harsh conditions.
  • Don't Use Pure Water: Avoid using only wateruse proper motorcycle coolant or a water/distilled water mix with rust inhibitors. Distilled water alone is acceptable only during flushing, not for long-term operation.

Pro Tips from MotoSport:

  • Always check coolant level before every ride, especially after a recent change or hard track use.
  • If you notice frequent coolant loss, inspect the radiator, hoses, and gaskets for potential leaks.
  • Seal up the system tightly and never overtighten the radiator cap—this can damage the neck and lead to pressure loss.

Your 1991 Honda CR125 is a high-performance machine—proper coolant maintenance preserves power, reliability, and engine longevity. For replacement parts, hoses, or radiators, MotoSport has you covered for every ride.

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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.