How to Change the Coolant in a 1991 Honda CR500

Shop parts for a 1991 Honda CR500 Dirt Bike.

The 1991 Honda CR500 is a legendary dirt bike known for its power, reliability, and distinctive two-stroke performance. Regular coolant changes are crucial to maintaining optimal engine temperature and preventing expensive damage – especially important for the high-performance CR500. This guide will walk you through a complete coolant change specific to your model, outlining key points all CR500 owners should be aware of to keep their machine performing its best.

Supplies You Will Need

  • New ethylene glycol-based coolant (compatible with aluminum radiators)
  • Drain pan
  • Metric socket set – commonly 8mm or 10mm for drain bolt
  • Replacement water pump crush washer (recommended)
  • Clean rags
  • Distilled water (optional for flushing)
  • Funnel
  • Gloves and eye protection

Step-By-Step Coolant Change Guide

  1. Ensure Engine is Cool: Never attempt to remove the radiator cap from a hot engine—let the bike cool completely first to avoid burns and pressurized coolant spray.
  2. Access Draining Points:
    • Remove the seat and tank, if necessary, for easier access to the radiator and hoses.
  3. Remove the Radiator Cap: With the engine cool, twist off the radiator cap to relieve pressure and allow the coolant to drain smoothly.
  4. Locate and Remove the Drain Bolt:
    • On the 1991 CR500, the coolant drain bolt is typically found at the bottom of the water pump cover on the right side of the engine.
    • Place your drain pan beneath this bolt.
    • Carefully remove the bolt and allow all coolant to drain. Inspect or replace the crush washer to ensure a tight seal when reinstalling.
    • Tip: Some owners also carefully loosen the lower radiator hose to maximize drainage.
  5. Flush the System (Optional):
    • Refit the drain bolt (with new washer, if available) and fill the system with distilled water.
    • Run the engine briefly, then allow it to cool and drain again. Repeat until the water runs clear for optimal flushing.
  6. Add New Coolant:
    • Tighten the drain bolt securely (but do not overtighten).
    • Slowly fill the radiator with new coolant made for aluminum radiators—an absolute must for your CR500's longevity.
    • Stop when fluid reaches the base of the radiator filler neck.
  7. Bleed Air from the System:
    • With the radiator cap still off, start the engine and let it idle for a few minutes. Gently squeeze the top radiator hose to help release trapped air, then top up coolant as needed.
    • Once bubbling subsides and the coolant level remains steady, replace the cap.
  8. Check and Top Off:
    • Once the engine has cooled after a ride, recheck both radiator and reservoir levels; add coolant if necessary. It's normal for the level to drop slightly as remaining air escapes the first time or two you ride the bike after a coolant change.

Special Notes for 1991 Honda CR500 Owners

  • Only use an ethylene glycol-based coolant formulated for aluminum components. Never substitute plain water or incompatible coolant types – these can cause corrosion or overheat the high-performance CR500 engine.
  • The CR500's two-stroke engine generates more heat than most dirt bikes – check and replace coolant every season or after any overheat event for best reliability.
  • If you notice repeated coolant loss, overheating, or unusual bubbling after bleeding the system, inspect for leaks or possible head gasket issues.
  • Never reuse a damaged or worn crush washer on the drain bolt, as this may result in leaks and engine damage.

Final Check

  • After your first ride, double-check for leaks and make sure coolant levels remain topped – this simple step is critical for long-term engine life.

Winterizing or storing your CR500? Drain the system and replace with proper antifreeze to prevent damage during freezing temperatures.

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Shop Radiator Hoses for a 1991 Honda CR500 Dirt Bike.

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.