How to Change the Coolant in a 1979 Kawasaki KX80

Shop parts for a 1979 Kawasaki KX80 Dirt Bike.

Keeping your 1979 Kawasaki KX80 running cool and reliably starts with regular coolant changes. While older two-stroke dirt bikes like the KX80 are rugged and simple by modern standards, their cooling system maintenance remains vital for consistent performance and preventing engine damage. Below, the MotoSport team details the process to safely and effectively change the coolant in your classic mini-motocrosser.

What Makes the 1979 KX80 Cooling System Unique?

The 1979 KX80 was one of Kawasaki’s early youth motocross bikes, featuring a basic yet effective liquid-cooled two-stroke engine. Unlike modern bikes with overflow reservoirs, this KX80 generally relies on a core radiator setup without extra tanks, and its cooling passages can be prone to deposit build-up over decades. Take extra care to thoroughly flush the system and examine hoses for age-related wear.

Before You Start

  • Allow the engine to cool completely before starting the service.
  • Work in a well-ventilated area and use gloves & eye protection.
  • Gather a new bottle of coolant compatible with aluminum radiators, a drain pan, a funnel, and basic metric hand tools.

Step-by-Step: Changing the Coolant

  1. Remove seat & side panels Accessing the radiator cap and drain bolt is easier with plastics out of the way.
  2. Remove the radiator cap Turn the cap counterclockwise. Never open when hot – pressure buildup can cause scalding.
  3. Place a drain pan beneath the bike Locate the coolant drain bolt, typically on the lower portion of the right engine case or at the bottom of the radiator.
  4. Remove the drain bolt Let old coolant fully flow into the pan. Slightly rock the bike upright to assist draining.
  5. Flush the system (strongly recommended) Reinstall the drain bolt, pour distilled water into the radiator, and drain again. Repeat until water runs clear to remove old coolant and debris. For neglected bikes, consider a mild vinegar solution flush for severe deposits.
  6. Inspect system components Check the radiator hoses and clamps for cracks, bulges, or leaks. Replace if needed.
  7. Install the drain bolt Ensure the sealing washer is intact. Tighten gently – these are small aluminum threads.
  8. Slowly fill the radiator Use a funnel and pour in fresh coolant, stopping when nearly full. Adding too quickly can trap air.
  9. Remove air bubbles Gently rock the bike side to side. Lightly squeeze hoses if possible. For the ’79 KX80 without a bleed screw, briefly start the bike with the radiator cap off. Let it idle – rev the engine a few times to help air escape. Shut off as soon as coolant starts to rise up the neck, and top off the radiator if necessary.
  10. Reinstall the radiator cap Press down and turn until secure.
  11. Wipe down, reinstall body panels & seat

Final Checks & Good Practices

  • Start the engine and let it reach operating temperature (about 5 minutes)
  • Watch for coolant leaks or abnormal boiling
  • Shut off, let cool completely, and recheck the coolant level – top up if needed
  • Inspect after your first ride to ensure no gradual leaks or low levels

What to Watch For on the 1979 KX80

  • Older bikes may suffer from internal corrosion – be alert for cloudy coolant, persistent overheating, or signs of head gasket issues (milky coolant, excessive steam)
  • Replace ancient hoses & radiator caps if rubber is cracked or hard; age can cause leaks that compromise cooling
  • Use only aluminum-safe, ethylene glycol-based coolant – never use plain tap water or automotive coolant with silicate additives, as these can clog or damage the radiator

With regular coolant changes, your vintage Kawasaki KX80 will keep its cool for many motos to come.

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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.