How to Change the Coolant in a 1985 Honda CR125

Shop parts for a 1985 Honda CR125 Dirt Bike.

Keeping your 1985 Honda CR125 running cool is vital for performance and longevity. Old coolant can cause overheating and internal corrosion, so learning the right way to change it is essential. Here is a step-by-step guide developed specifically for MotoSport customers, with model-specific tips to keep your classic CR125 in prime shape.

Preparation

  • Allow the engine to cool completely before startinghot coolant can cause burns.
  • Place the bike on a stable stand, ideally outdoors or above a drain pan to catch fluid.
  • Gather a 10mm wrench, a funnel, a drain pan, a new crush washer for the drain bolt, and fresh coolant approved for aluminum engines. Distilled water is ideal for mixing if needed, as it prevents mineral build-up and corrosion.

Step 1: Locate and Open the Radiator Cap

  • The 1985 CR125 features scooped radiators on each side of the frame. The cap is located at the top of the left-side radiator.
  • Slowly remove the cap to relieve system pressure.

Step 2: Remove the Drain Bolt

  • Locate the coolant drain bolt at the bottom of the water pump cover on the right side of the engine case near the kickstarter.
  • Place the drain pan beneath the bolt and remove it carefully. The coolant will drain quickly, so be prepared.
  • Inspect the crush washerreplace it with a new one to prevent leaks during reassembly.

Step 3: Flush the System (Optional but Recommended)

  • For best results, pour a small amount of distilled water into the radiator and reinstall the drain bolt temporarily.
  • Start the bike and let it idle for a minute to circulate. Shut the engine down, let it cool, then drain the water out again.

Step 4: Reinstall the Drain Bolt

  • Insert the drain bolt and tighten it snugly (do not overtighten; this part is aluminum and threads can strip).
  • Confirm the crush washer is seated correctly to prevent leaks.

Step 5: Add New Coolant

  • Using a funnel, fill the radiator slowly with coolant. For best results, use 50/50 premix made for aluminum engines, or mix coolant concentrate with distilled water as specified on the bottle.
  • Fill until coolant reaches the neck of the radiator. On the CR125, there's typically no overflow reservoir, so fill just to the bottom of the cap's internal sealing surface.
  • Gently squeeze the radiator hoses to help purge air from the system.

Step 6: Bleed Air and Top Off

  • With the cap still off, briefly start the engine and let it idlewatch for bubbles escaping as air purges from the cooling system.
  • If coolant level drops, top it off to the correct height.
  • Shut off the engine and reinstall the radiator cap securely.

Step 7: Final Inspection

  • Check under the bike for leaks at the water pump drain bolt and along radiator hoses.
  • After the first ride, re-inspect coolant level and add more as needed.

Model-Specific Tips for the 1985 Honda CR125

  • This model uses a simple, open cooling system with no overflow bottle–overfilling may lead to spillage when hot.
  • If you notice persistent coolant loss or contamination, inspect the water pump (a known weak spot) for leaks or worn seals. A failing water pump can quickly cause overheating and engine damage.
  • Avoid using hard tap water. Deposits from impurities can block the narrow passages in the cylinder head and radiators, overheating your bike.
  • When bleeding air, ensure the cylinder head and top of the left radiator are the high point in the system for the most effective purge.
  • Allow the engine to properly warm up after coolant changes. This ensures any remaining air is pushed out during those first few heat cycles—top off as needed.

Changing your coolant every one to two seasons, or after major engine work, keeps your vintage CR125 performing its best and helps prevent corrosion in the lightweight magnesium and aluminum parts. For all the parts and fluids you need, MotoSport has your 1985 Honda CR125 covered.

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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.