How to Change the Coolant in a 1983 Kawasaki KX125

Shop parts for a 1983 Kawasaki KX125 Dirt Bike.

Changing the coolant on your 1983 Kawasaki KX125 is essential for maintaining performance, preventing overheating, and protecting the engine components. This classic motocross machine uses a liquid-cooled 2-stroke engine, so clean coolant plays an especially critical role. Below, find a step-by-step guide created specifically for this modelwith owner considerations you will not want to miss.

Recommended Coolant & Capacity

  • Use a permanent type of antifreeze designed for aluminum engines and radiators (green in color), containing ethylene glycol with corrosion and rust inhibitors.
  • Mix coolant 50% with soft water (distilled preferred). Pre-mixed solutions are also acceptable.
  • Total system capacity: 0.96 liters (just under 1 liter).

Tools & Supplies Needed

  • Phillips and flathead screwdrivers
  • Pliers
  • Catch pan for old coolant
  • Funnel
  • Gloves and safety glasses
  • Clean rags
  • Fresh coolant as specified above

Step-by-Step Coolant Change Instructions

  1. Prepare the bike. Ensure the engine is completely cooled down before starting. Never open the radiator cap or drain coolant from a hot engine—the system is pressurized and can cause burns.
  2. Remove the radiator cap (located on the top of the left-side radiator). Do so in two steps: first, turn the cap to the first stop to release pressure, pause, then push down and turn further to remove it.
  3. Locate the coolant drain bolt or lowest hose on the water pump cover.
    • Position a catch pan below. Loosen and remove the bolt (or hose clamp), allowing old coolant to fully drain.
    • Inspect the drained fluid for rust or debris—contaminants may signal the need for additional flushing or inspection of system components.
  4. Flush (optional). If the previous coolant was severely contaminated, fill the system with distilled water, warm the bike briefly, then let it cool and re-drain.
  5. Inspect hoses and connections. On the 1983 KX125, original hoses can become brittle with age. Inspect for cracks or bulges. Replace any suspect hoses before refilling.
  6. Reinstall drain bolt/hose and securely tighten the clamp or bolt.
  7. Refill with new coolant.
    • Position the bike upright and pour coolant into the radiator filler until it reaches just below the filler neck.
    • Slowly fill, pausing to allow air bubbles to escape. Rock the bike gently side-to-side to help release trapped air.
  8. Bleed air from the system.
    • Start the engine and let it idle with the radiator cap off. Watch for air bubbles rising out – add coolant if the level drops.
    • Once the coolant stops bubbling out, top up and reinstall the cap.
  9. Check the overflow bottle (if equipped). Fill to the marked upper line. If absent, monitor the radiator level as referenced above.
  10. Run the bike through a full heat cycle, then allow it to fully cool down. Re-check the coolant level in the radiator and add as necessary. If the system continues to lose coolant or air bubbles persist after multiple cycles, further system inspection may be necessary.

KX125 Owner Tips & Special Notes

  • The aluminum radiators on the 1983 KX125 are prone to internal corrosion if the wrong coolant mixture is used. Always use the recommended 50/50 pre-mix for optimal protection.
  • OEM radiator caps are rated for 95 – 125 kPa. If your cap is original, consider testing or replacing it — aged caps can cause pressure loss, leading to boil-over or insufficient cooling.
  • This model has no coolant temperature warning light. Monitor engine temperature by feel and watch for visible steam or excessive heat from the radiators during use.
  • Always dispose of used coolant responsibly according to local regulations.

Proper coolant maintenance keeps your 1983 KX125 running cool, extends the life of the engine and cooling system, and helps you get the most out of every ride.

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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.