How to Change the Coolant in a 2018 Yamaha YZ125
Shop parts for a 2018 Yamaha YZ125 Dirt Bike.
Proper coolant maintenance is vital for keeping your 2018 Yamaha YZ125 running cool and reliable out on the track or trail. Changing the coolant not only prolongs the life of your engine, but it also protects the aluminum components from corrosion. Here is a step-by-step proprietary MotoSport guide specifically for the YZ125 owner, including unique model pointers.
What You'll Need
- Socket wrench (8mm typically fits the drain bolt)
- Drain pan
- Distilled water (for flushing)
- Funnel
- New coolant (Yamaha recommends a high-quality ethylene glycol-based coolant)
- Shop towels or rags
- Safety gloves and eyewear
Important Notes for the 2018 YZ125
- The YZ125 features a lightweight aluminum radiator system. Always use coolants intended for aluminum engines to avoid internal corrosion.
- Never remove the radiator cap when the engine is hot—let it cool down fully to prevent burns and coolant spray.
- Check and replace coolant every 1-2 years or after about 40-50 hours of riding, especially if you ride in muddy or sandy conditions where radiator efficiency can be compromised.
Step-by-Step Coolant Change Process
- Ensure your YZ125 is completely cool. Remove the seat and plastics if they restrict radiator access.
- Place your drain pan under the engine and locate the coolant drain bolt. For the 2018 YZ125, this bolt is at the lowest point of the water pump cover on the engine’s right side.
- Remove the radiator cap to allow air in for better draining.
- Loosen the coolant drain bolt using the 8mm socket. Allow all old coolant to drain completely into your pan.
- With the drain bolt still out, flush the system by slowly pouring distilled water through the radiator neck. This helps remove remaining old coolant and debris.
- Reinstall the drain bolt securely (do not over-tighten as the water pump cover is aluminum).
- Pour in fresh coolant via the radiator fill neck using the funnel. Fill until the coolant reaches just below the neck. If your model has an overflow reservoir, check and fill to the designated line.
- Start the engine and let it idle for a few minutes with the radiator cap off. Gently rock the bike side to side to release any trapped air bubbles. Top off the coolant as needed.
- Turn off the engine and reinstall the radiator cap tightly.
- Check for leaks around the water pump and drain bolt. Wipe away any spilled coolant.
Post-Service Inspection
- After your next ride, double check the coolant level with the engine cool and top off if needed.
- Inspect hoses and the radiator for signs of leaks or damage, as hard riding can loosen clamps over time.
YZ125-Specific Tips
- The 2018 YZ125’s high-revving two-stroke engine generates more heat than you might expect from its displacement—prompt coolant replacement is particularly important for preventing overheating on long motos.
- If you frequently ride sandy tracks, clean the radiator fins regularly to maintain ideal airflow and cooling efficiency.
Staying on top of coolant changes is one of the most effective ways to keep your YZ125 running crisp, fast, and trouble-free. Refer to your YZ125 service manual for torque specs and always use quality parts available at MotoSport when servicing your bike.
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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.