How to Change the Coolant in a 2001 Honda CR125 – Step-by-Step Guide

Shop parts for a 2001 Honda CR125 Dirt Bike.

Keeping your 2001 Honda CR125 running cool is critical for optimal engine life and performance. While changing the coolant is straightforward, attention to detail is especially important on this classic two-stroke. Follow these detailed instructions to perform a complete coolant replacement, and note a few unique factors about this legendary model along the way.

Tools & Supplies Needed

  • 10mm socket or wrench
  • Drain pan or bucket
  • New coolant (glycol-based, premixed or to be mixed with distilled water)
  • Funnel
  • Clean rag
  • New copper washer for drain bolt (optional, but recommended)

Step 1: Preparation – Cool Engine & Safety

Ensure the bike is completely cool before you work. Place the bike on a stand and position your drain pan under the water pump area. Clean the top of the radiator cap to prevent dirt from falling in.

Step 2: Remove the Radiator Cap

Dispose of pressure by slowly removing the radiator cap. This step lets air in so the coolant drains thoroughly.

Step 3: Locate & Remove the Drain Bolt

On the 2001 CR125, the coolant drain bolt is found on the lower water pump cover. Use a 10mm socket to remove this bolt. Allow coolant to drain fully into your pan. A tip: Hold the bike upright or gently rock it to get all the fluid out.

Step 4: Inspect & Replace Drain Washer (Optional)

If the copper washer on the drain bolt looks worn, replace it now for a proper seal. Thread the drain bolt back in and torque to about 10 Nm for a secure fit.

Step 5: Flush (Optional but Recommended)

For extra peace of mind, you can flush the system by filling with distilled water, running the bike briefly, then draining again. Repeat if fluid appears cloudy or discolored.

Step 6: Refill Coolant

Using a funnel, pour high-quality premixed coolant (or mix with distilled water; never tap water, to prevent mineral buildup) into the radiator. Fill until coolant reaches just below the bottom of the cap seat. If you're riding harsh conditions, consider a coolant with added water-wetter for better heat transfer.

Step 7: Bleed & Top Off

Tilt the bike side to side to release trapped air. Briefly start the engine with the radiator cap off, letting air bubbles escape, then shut off and top up as needed. Replace cap, ensuring it is locked down securely.

Step 8: Check for Leaks & Test Ride

Inspect for leaks at the drain bolt and hoses. After a short ride, let the engine cool and check the coolant level again. Top off if necessary, as the system can burp out excess air after initial use.

Owner Notes: What Makes the 2001 CR125 Unique

  • The 2001 CR125 uses a magnesium water pump cover, which can corrode if improper coolant or mixed metals are present. Always use the recommended glycol-based motorcycle coolant and replace the copper washer to avoid leaks and corrosion issues unique to these magnesium cases.
  • Inspect cylinder head nuts and radiator cap regularly. Overheating in this model is often caused by weak caps or loose head nuts—a common quirk of CR125s.
  • If racing or riding hard, regular coolant changes and system checks help mitigate the model's natural tendency toward high operating temperatures in extreme conditions.

Routine maintenance like a coolant flush keeps your 2001 Honda CR125 running cool and performing at its best—an easy job that pays back every time you hit the track or trails.

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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.