How to Change the Coolant in a 1990 Kawasaki KX250

Shop parts for a 1990 Kawasaki KX250 Dirt Bike.

Routine coolant changes are vital for your 1990 Kawasaki KX250’s engine health. The KX250’s radiator and water pump system are designed to keep the high-revving two-stroke engine at optimal temperature, so following the correct procedure ensures maximum performance and longevity. Here’s a MotoSport exclusive step-by-step guide tailored to your classic dirt bike.

Preparation

  • Work only when the engine is totally cool to avoid burns–never remove the radiator cap when hot.
  • Place your KX250 on a stand so the bike is stable and upright for a thorough drain.
  • Gather a drain pan, a fresh washer for the drain bolt, and the correct coolant. A 50/50 water and ethylene glycol blend (formulated for aluminum radiators) is recommended.

Draining Old Coolant

  • Remove the radiator cap to allow air into the system.
  • Locate the coolant drain bolt on the right side of the cylinder near the water pump cover. Place your drain pan directly below it.
  • Unscrew the drain bolt (an 8mm bolt with a washer underneath) to start draining. Some coolant may still be trapped inside the cylinder, so allow time for complete drainage. If your bike has a second drain (sometimes found on the cylinder), remove that as well to ensure a full flush.
  • Immediately clean any coolant that spills onto other parts to avoid corrosion and residue buildup.

Flushing the System (Recommended)

  • For optimal maintenance, pour some distilled water into the radiator, reinstall the drain bolt gently, and run the engine briefly. Then repeat the drain process. This helps remove any lingering debris or old coolant from inside the water jacket and radiator channels.

Refilling with Fresh Coolant

  • Reinstall the drain bolt with a new washer to prevent leaks. Tighten securely but avoid overtightening the small bolt threads.
  • Pour coolant into the radiator until it nearly reaches the base of the filler neck–the KX250 uses approximately 0.96 liters (1 US quart) of coolant.
  • Slowly rock the bike side to side and gently squeeze the radiator hoses to help release trapped air.

Bleeding Air Out of the System

  • Start the engine with the radiator cap off and let it idle, keeping an eye on the coolant level. Add coolant if it drops as air escapes.
  • Once air bubbles stop appearing and coolant starts to expand or bubble up, install the radiator cap before it overflows.
  • Allow the engine to reach full operating temperature, then shut it off and let it cool completely back to ambient.
  • Check the coolant level again in both radiator and overflow bottle (if equipped). Top off as needed.

Special Notes for the 1990 Kawasaki KX250

  • The 1990 KX250 is known for its high-revving two-stroke engine and lightweight chassis, making cooling system function crucial–overheating can quickly damage the cylinder and head gaskets if coolant service is neglected.
  • If changing the coolant for the first time on a vintage machine, inspect all hoses, the radiator cap, and the water pump seal for leaks or deterioration&ndash-old rubber parts can fail unexpectedly and are worth replacing for peace of mind.
  • Always use coolants compatible with aluminum to protect the KX250’s radiators and engine from corrosion.

With fresh coolant and a properly bled system, your 1990 Kawasaki KX250 is ready for its next ride–confident that its legendary two-stroke performance stays cool under pressure.

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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.