How to Change the Coolant in a 1986 Kawasaki KX250

Shop parts for a 1986 Kawasaki KX250 Dirt Bike.

Regularly changing the coolant in your 1986 Kawasaki KX250 is critical for optimal performance and longevity. Proper coolant maintenance prevents overheating, corrosion, and engine damage, especially on a classic model like the KX250. Follow these step-by-step instructions designed specifically for MotoSport customers to keep your 2-stroke running strong.

What You Need

  • Coolant recommended for aluminum engines
  • Socket wrench set (8mm socket for drain bolt)
  • Drain pan
  • Funnel
  • Clean shop towels
  • Protective gloves

Step-by-Step Coolant Change Guide

  1. Ensure Engine is Cool
    Never work on a hot engine. Allow the KX250 to completely cool down to prevent burns and avoid cracking the radiator or engine components.
  2. Access the Radiator Cap
    Remove the seat and tank shrouds if needed for better clearance. Unscrew and set aside the radiator cap.
  3. Locate and Remove the Drain Bolt
    On the 1986 KX250, the coolant drain bolt is usually situated on the lower part of the water pump cover on the right side of the engine (use an 8mm socket). Place a drain pan underneath and remove the bolt.
    For thorough draining, gently tip the bike to the opposite side.
  4. Finish Draining
    Open the radiator cap if you have not done so already. Let all coolant flow out. Check for any secondary cylinder drain bolts, as some models include theseremoving them ensures complete drainage.
  5. Reinstall the Drain Bolt(s)
    Clean and reinstall the drain bolt and washer. Do not overtighten to avoid damaging the threads.
  6. Flush if Needed
    If switching coolant types or if residue is present, briefly flush the system with distilled water and repeat the drainage process.
  7. Refill with Fresh Coolant
    Using a funnel, pour new coolant slowly into the radiator until it reaches the top of the filler neck. Wait for any bubbles to rise and top off as needed. This 2-stroke does not have a separate coolant reservoir.
  8. Bleed the Cooling System
    Lean the bike from side to side to release trapped air pockets. Squeeze radiator hoses gently to help move air up. Fill again if the level drops.
  9. Warm the Engine
    Start the engine and let it idle with the radiator cap off. Watch for the level to drop as coolant circulates and air escapes; top off again. Shut off once it stabilizes and no more bubbles appear.
    Carefully reinstall the radiator cap.
  10. Inspect for Leaks & Reassemble
    Check the drain bolt and all hoses for signs of leaking. Reinstall any bodywork, and wipe away spillage.

1986 KX250 Model Notes

  • This Kawasaki generation features lightweight aluminum radiators. Inspect for bent fins or leaks – high-quality replacement radiators are available if needed.
  • The two-stroke engine relies on effective cooling. Consistently low coolant can lead to seizure – check levels routinely during the riding season.
  • Use coolant formulated for aluminum and magnesium to prevent electrolysis and internal corrosion, especially with the magnesium water pump covers common on this era KX250.
  • Factory hoses and clamps tend to harden or corrode over time—if your originals are brittle or leaking, replace them proactively.

Final Recommendations

Changing the coolant annually is recommended, particularly if you race, ride hard, or use the KX250 in demanding conditions. With these steps, your classic Kawasaki will run cooler, last longer, and deliver peak power in every moto.

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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.