How to Change the Coolant in a 1989 Yamaha YZ125
Shop parts for a 1989 Yamaha YZ125 Dirt Bike.
Maintaining the cooling system on your 1989 Yamaha YZ125 is critical for top engine performance and longevity. If your bike has seen roughly 40 to 50 hours of runtime or you are due for scheduled maintenance, it's time to replace the coolant. Below is a step-by-step proprietary MotoSport.com guide tailored to the unique requirements of your vintage YZ125.
Tools & Supplies Needed
- Fresh coolant (high-quality ethylene glycol type, safe for aluminum)
- Soft or distilled water for mixing (if necessary)
- Socket wrench 8mm for drain bolt
- Drain container
- Funnel
- Torque wrench
- Clean rags
Preparation – Essential Safety
- Ensure the engine is completely cool before starting—never open the radiator cap on a hot engine.
- Park the bike on a level surface and use a stand for stability.
- Remove any bodywork or guards that obstruct access to the radiator or drain bolt.
Drain the Old Coolant
- Locate the coolant drain bolt (bottom of the water pumpleft side of engine).
- Place the drain container under the engine.
- Slowly loosen and fully remove the radiator cap to release residual pressure.
- Remove the drain bolt and allow coolant to fully drain.
- Inspect the copper washer on the drain bolt for damage; replace if needed.
- Flush the system with clean tap water to remove residue if the old coolant was contaminated.
Reinstall & Torque the Drain Bolt
- Reinstall the copper washer and drain bolt.
- Tighten the bolt to 10 Nm (1.0 m·kg, 7.2 ft–lb) to avoid leaks or thread damage.
Refill with New Coolant
- Mix coolant and soft/distilled water 50/50 if not pre-mixed.
- Slowly pour coolant through a funnel into the radiator until the fluid reaches the base of the radiator neck. The specified capacity is 0.95 L.
- Gently tap the hoses and radiator to help release trapped air.
- Reinstall the radiator cap securely.
Bleed Air & Final Checks
- Start the engine and let it idle for several minutes. Monitor the coolant level as air bubbles escape—top off if necessary after shutting the engine off and cooling.
- Inspect thoroughly for leaks at the drain bolt and hoses.
- Wipe up any spilled coolant immediately as it is corrosive and harmful to paint and the environment.
Special Notes for 1989 Yamaha YZ125 Owners
- This model features a liquid-cooled, two-stroke engine highly sensitive to cooling system neglect. Overheating can quickly damage aluminum engine components.
- Never use hard or salt water in your coolant mixture, as it will corrode internal passages.
- Replace coolant every two years, or sooner under heavy race use.
- Check hoses and clamps for age-related cracks or wear every service interval—upgrade to modern silicone hoses for improved durability if desired.
For genuine replacement parts or upgrades, always use trusted factory components to guarantee the best fit and cooling performance for your vintage motocrosser.
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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.