How to Change the Coolant in a 1990 Kawasaki KX500

Shop parts for a 1990 Kawasaki KX500 Dirt Bike.

The 1990 Kawasaki KX500 is a legendary open-class two-stroke known for its power – keeping this machine reliable depends on proper maintenance, especially caring for the cooling system. Regular coolant changes prevent overheating and protect internal engine components from corrosion and mineral build-up. This proprietary MotoSport guide gives you step-by-step instructions for changing coolant on your KX500, plus key model-specific insights every owner should know.

What You Need

  • Fresh coolant (compatible with aluminum radiators; never use plain water long term)
  • Phillips screwdriver and 8 mm socket or wrench
  • Drain pan
  • Clean rag
  • Protective gloves and eyewear

Step-by-Step Coolant Change Guide

  1. Let the engine cool completely. Never open the radiator cap when the engine is hot to avoid possible burns.
  2. Remove the seat and radiator shrouds if necessary for access.
  3. Place the drain pan under the water pump area, on the right side of the motorcycle.
  4. Remove the radiator cap. Slowly turn it to the first stop to release pressure, then fully remove.
  5. Locate the coolant drain bolt. On the KX500, this is typically on the lower side of the water pump cover. Use the 8 mm socket to remove it. Some models may have a copper washer – do not lose it.
  6. Allow all coolant to drain completely. Tilting the bike slightly side-to-side can help evacuate hidden coolant in hoses and the cylinder head.
  7. Unfasten the radiator lower hose (optional, but helps with a better flush). Remove and pour out any remaining coolant.
  8. Reinstall the drain bolt (with washer). Torque snug, but do not overtighten to avoid stripping threads. If the washer shows sign of damage, replace it.
  9. Fill the radiator with fresh coolant up to the base of the filler neck. For best protection, use a premixed motorcycle coolant appropriate for mixed-metal cooling systems.
  10. Bleed air from the system:
    • Tilt/bounce the bike gently side-to-side to release trapped bubbles.
    • With the radiator cap off, start the engine and let it idle for a couple of minutes. Watch the coolant level and top up if it drops.
    • When bubbles stop appearing and the level stabilizes, turn off the engine and top off again.
    • Replace the radiator cap securely.
  11. Check coolant level after first heat cycle: Ride the bike until fully warm, then let it cool completely and recheck coolant level. Top up as needed, as any hidden air pockets may purge out.
  12. Inspect for leaks and install plastics. Wipe up any spilled coolant. Dispose of old coolant responsibly – do not pour it down drains or onto the ground.

Special Tips for the 1990 KX500

  • The KX500's high-performance two-stroke engine generates significant heat under load. Never run low on coolant, and use the correct radiator cap (rated 14–18 psi) to ensure proper pressure.
  • The stock aluminum radiator can clog or corrode if you use plain water or incompatible coolants – always run a high-quality, motorcycle-approved coolant.
  • Inspect radiator fins for debris and carefully straighten bent fins as needed. Clean exterior surfaces using a soft brush, not high-pressure water, which can damage fins.
  • The coolant drain bolt and radiator mounts are made of aluminum; overtightening may strip the threads.
  • Periodic replacement of the radiator cap and coolant hoses is recommended, especially for a vintage model like the 1990 KX500.

Keep Your KX500 Running Cool

Coolant service is basic, but crucial: skipping it risks serious, costly damage. Regularly inspect and maintain your cooling system, especially if you ride aggressively or in hot, slow terrain. For genuine replacement parts – including radiators, hoses, and gaskets – trust MotoSport to keep your Kawasaki KX500 in peak condition.

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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.