How to Change the Coolant in a 1980 Yamaha YZ125
Shop parts for a 1980 Yamaha YZ125 Dirt Bike.
Maintaining the correct coolant levels is essential for keeping your 1980 Yamaha YZ125 performing at its best. Regular coolant changes prevent overheating, corrosion, and wear inside your engine – especially critical for the high-revving, air-assisted liquid-cooled system of the YZ125 from this era. Here's a step-by-step guide designed specifically for your vintage two-stroke.
What You’ll Need
- Fresh high-quality ethylene glycol-based coolant (with anti-corrosion agents for aluminum engines)
- Distilled water (for flushing)
- Drain pan
- 8mm socket or wrench (for drain bolt)
- Copper washer (replace if damaged)
- Funnel
- Protective gloves and eyewear
Steps for Changing Coolant
- Cool the Bike: Always ensure your engine is completely cool before working on the cooling system.
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Access and Drain: Remove the radiator cap. Position a drain pan under the engine near the water pump. Loosen the coolant drain bolt (typically located on the lower side of the water pump cover) and allow old coolant to completely drain out. Remove the copper washer and inspect it—replace if damaged.
YZ125 tip: Coolant capacity for the 1980 model is approximately 0.95 liters. - Flush (Optional but Recommended): Reinstall the drain bolt loosely, fill the system with distilled water, and run the engine for a few minutes. Drain again to clear any old coolant or debris. Repeat if the drained liquid is still dirty.
- Sealing Up: Tighten the drain bolt to 10 Nm (7.2 ft–lb). Over-tightening can strip the aluminum threads.
- Refill: Using your funnel, fill the radiator slowly with a 50/50 mix of coolant and distilled water until the level reaches the bottom of the radiator neck. The correct chemistry protects your YZ125’s aluminum cylinder and head from corrosion.
- Burp the System: With the radiator cap off, start the bike and let it idle briefly. Gently rock the bike or blip the throttle to release trapped air bubbles. Add coolant as the level drops.
- Finishing Up: Once the coolant stabilizes at the top of the neck and no more bubbles rise, reinstall the radiator cap securely. Wipe off spills, reinstall any body panels, and dispose of used coolant responsibly.
- Inspection: After your next ride, check the coolant level (when cool) and top off as necessary.
Special Notes for 1980 Yamaha YZ125 Owners
- This model uses a simple, open vent radiator system without a coolant reservoir—always check levels at the cap, not in a bottle.
- Avoid running straight water. Use only soft or distilled water in your coolant mix to prevent mineral deposits.
- The original radiator and hoses can become brittle over decades; inspect for signs of aging or cracks, as these will affect cooling performance.
- Plan coolant changes every 40–50 hours of ride time or every season for best protection.
Stay on top of coolant changes, and your classic YZ125 will be ready to conquer the track for years 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.