How to Change the Coolant in a 1978 Yamaha YZ250

Shop parts for a 1978 Yamaha YZ250 Dirt Bike.

The legendary 1978 Yamaha YZ250 features a liquid-cooled two-stroke engine that requires proper coolant maintenance for optimal performance and longevity. Regular coolant changes prevent corrosion, overheating, and engine damageespecially important on a vintage race machine like the 78 YZ250. Below, follow this dedicated MotoSport guide to correctly change the coolant and keep your classic YZ250 running strong.

What You Need

  • High quality ethylene glycol anti-freeze with anti-corrosion for aluminum engines (50–50 mix with soft water recommended)
  • Clean tap water for flushing
  • Catch pan/container
  • Basic hand tools (sockets, wrenches, screwdriver)
  • Rags for cleanup

Step-by-Step Coolant Change Procedure

  1. Allow the engine to cool completely before beginning. Never open the radiator cap on a hot engine to avoid serious burns.
  2. Position the bike upright on a stable surface and place a catch pan under the engine area.
  3. Remove the radiator cap to break any vacuum and facilitate draining.
  4. Locate and remove the coolant drain bolttypically found on the lower engine or water pump housing. Keep track of the copper washer.
  5. Allow all coolant to drain fully into your pan. Dispose of old coolant safely; it is toxic and harmful to the environment.
  6. Flush the system by reinstalling the drain bolt temporarily and filling the radiator with clean tap water. Start the bike briefly, run for one to two minutes, then shut down and drain again. Repeat if the water comes out dirty or colored.
  7. Reinstall the drain bolt with its copper washer, tightening to approximately 10 Nm (7.2 ft-lb).
  8. Fill the radiator to the base of the filler neck with the 50–50 coolant-water mixture. For the 1978 YZ250, total coolant capacity is about 1.20 liters (1.27 US quarts).
  9. Start the engine and allow it to reach operating temperature. This works out any remaining air pockets in the system. During this time, lightly rock the bike or squeeze hoses gently to help purge air.
  10. Let the bike cool off completely, then check and top off coolant as necessary to the correct level.
  11. Inspect for leaks and ensure all fasteners are tight.

Special Notes for the 1978 YZ250 Owner

  • This model is among the earliest liquid-cooled motocross bikes. Always use high-quality, aluminum-safe coolant to prevent corrosion in older radiators and cylinder heads.
  • Be gentle with plastics and rubber hoses. Age may have made them brittle—if you notice cracks or swelling, replace parts promptly to avoid catastrophic failures during rides.
  • After the coolant change, recheck levels after the first ride. Small air pockets may work out during the first heat cycle, requiring a minor top-off.
  • Always monitor for persistent coolant loss. Repeat drain-reservoir-empty cycles may signal a bigger issue, like a damaged gasket or pinhole leak.

Pro Tip

Keep a maintenance log. Documenting coolant changes allows you to keep track of service intervals and spot any recurring cooling system issues in your vintage YZ250.

Stay ahead of maintenance and enjoy the legendary snap of your YZ250 engine with cool confidence.

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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.