How to Change the Coolant in a 1990 Kawasaki KX80 Big Wheel

Shop parts for a 1990 Kawasaki KX80 Big Wheel Dirt Bike.

The 1990 Kawasaki KX80 Big Wheel is a competitive two-stroke motocross machine designed for youth riders seeking the perfect blend of nimble handling and added stability from its oversized 16-inch rear and 19-inch front wheels. Keeping its cooling system in top condition protects the high-performance engine from heat-related wear, especially during hard riding. Below is a step-by-step, model-specific guide from MotoSport to keep your KX80BW running cool lap after lap.

What You Need

  • Approved motorcycle coolant (pre-mixed or distilled water and concentrated as specified by your coolant; never use tap water due to mineral deposit risk)
  • Drain pan
  • Socket set (8mm commonly fits the drain bolt)
  • Funnel
  • Rubber gloves and shop rags
  • Replacement sealing washer (recommended)

Step 1: Prepare the Bike

  • Ensure the engine is completely cool. This is essential to prevent burns and avoid pressure spray from the system.
  • Place the bike securely on a stand for level access to the drain plug and radiator cap.

Step 2: Remove the Radiator Cap

  • Carefully unscrew the radiator cap to release any residual pressure. This improves flow during draining and prevents vacuum lock in the system.

Step 3: Locate & Remove the Drain Bolt

  • On the left side of the engine, find the coolant drain bolt located at the base of the water pump cover. This usually has a sealing washer that should be replaced for each service.
  • Place your drain pan beneath the area and loosen the bolt. Allow the coolant to fully drain from the system.
  • If equipped, open the radiator cap overflow tube or expansion tank to speed draining and ensure the system empties completely.

Step 4: Inspect & Refit the Drain Bolt

  • Inspect and replace the sealing washer if it shows wear or flattening, then thread the drain bolt by hand to avoid cross-threading before tightening securely.

Step 5: Fill the Radiator with Coolant

  • Using a funnel, slowly fill the radiator with your chosen coolant blend up to the bottom of the filler neck. Pour gradually and pause occasionally to allow trapped air to escape.
  • Some KX80 bikes may have a bleed screw on the cylinder or radiator. If present, briefly loosen this screw until coolant flows, then tighten it again to release any stubborn air pockets.

Step 6: Burp and Top-Off the System

  • With the cap still off, start the engine and let it idle for 1–2 minutes. Occasionally blip the throttle and gently rock the bike side to side to help air bubbles escape from the system.
  • Shut off the engine. The coolant level may drop as trapped air purges—top off as needed to the base of the filler neck.
  • If your model has an overflow or expansion tank, fill to the indicated "upper" line.

Step 7: Secure All Components

  • Wipe away any spills and ensure the radiator cap and drain bolt are tightly secured.
  • Inspect hoses for cracks or leaks and replace with OE or high-quality aftermarket parts if necessary.

Step 8: Test Ride and Monitor

  • Run the bike fully up to operating temperature and check for leaks. Allow it to cool and re-check the coolant level, topping off if necessary. Monitor the level after subsequent rides for the first few hours.

KX80 Big Wheel Specific Notes

  • The Big Wheel variation features a slightly larger radiator for the increased cooling needs of its larger wheels and youthful performance tuning. Always use coolant rated for aluminum radiators to avoid corrosion.
  • Original radiators and hoses may be showing age. Inspect them for damage or softness when performing coolant service—early replacement can help avoid mid-ride breakdowns.
  • This model requires regular cooling system maintenance, especially if operated in muddy or sandy conditions, as debris can clog cooling fins and reduce effectiveness.
  • The 2-stroke engine does not tolerate overheating—keep a close eye on overheating symptoms, such as steam from the radiator or power drop.

Coolant Change Interval

  • For optimal engine health, MotoSport recommends changing the coolant at least once a year, or more often if you ride in extreme conditions.

MotoSport has all the parts and coolant you need to keep your 1990 Kawasaki KX80 Big Wheel running at its best.

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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.