How to Change the Coolant in a 1981 Honda CR250

Shop parts for a 1981 Honda CR250 Dirt Bike.

The 1981 Honda CR250 is a classic among moto enthusiasts and a staple in two-stroke performance. Maintaining your cooling system is vital to keep this vintage machine running at peak performance – especially considering the unique requirements and age of early '80s CR models.

Follow this step-by-step proprietary MotoSport guide to changing the coolant on your 1981 CR250:

Preparation

  • Work with the engine cold to avoid burns.
  • Place the bike securely on a stand for stability.
  • Remove the seat and side panels for unrestricted access to the radiator and water pump area.
  • Have a drain pan, new coolant (a high-quality ethylene glycol-based or dedicated motorcycle coolant), proper tools, and safety gloves ready.

Draining the Old Coolant

  • Remove the radiator cap slowly to relieve any residual pressure.
  • Locate the coolant drain bolt on the water pump cover (usually a 10mm bolt on the lower side of the engine case).
  • Position your drain pan below the water pump bolt.
  • Carefully remove the drain bolt and let all old coolant flow out. Inspect the bolt washer and replace if necessary for a proper seal.
  • For a thorough flush, you can remove the lower radiator hose and allow any trapped fluid to escape.

Flushing the System (Recommended for Older Models)

  • Pour distilled water into the radiator, reinstall the drain bolt, and briefly run the engine to circulate (15–30 seconds maximum) – do not let it overheat.
  • Turn off, let cool, and drain again to clear out residue and scale built up from older coolant.
  • Repeat if needed until water runs clear.

Refilling with New Coolant

  • Install the drain bolt with its washer snugged to spec – do not overtighten on the aluminum case.
  • Slowly fill the radiator with fresh coolant up to the base of the filler neck. Gently rock the bike to dislodge trapped air bubbles.
  • Reinstall the radiator cap loosely at first. Start the engine and let it idle to full operating temperature so the thermostat opens and coolant circulates. Some air may purge into the overflow – this is normal.
  • Shut the engine off, allow to cool completely, and recheck the coolant. Top up if necessary at both filler and reservoir for proper system function.

Inspection & Important Model-Specific Tips

  • Check all hose connections for leaks and inspect for dry rot or cracks – vintage rubber parts on 1981 bikes often need replacement.
  • Monitor the temperature on the first ride after the change to confirm successful air bleeding. The early CR250s do not have a temperature gauge, so pay attention to engine performance and unusual sounds.
  • If your radiator cap shows signs of wear, replace it to ensure the coolant system holds correct pressure.
  • OEM specifications for coolant capacity and radiator pressure should always be referenced, as the 1981 CR250 design lacks modern overflow tank conveniences. Never overfill.

Replacing coolant is simple preventative maintenance, especially critical on competitive vintage models like the 1981 Honda CR250. Properly flushed and filled coolant systems protect against overheating – so you can keep riding hard, lap after 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.