How to Change the Coolant in a 2018 Yamaha TTR125L: MotoSport Guide

Shop parts for a 2018 Yamaha TTR125L Dirt Bike.

Maintaining the proper coolant levels in your 2018 Yamaha TTR125L is essential for engine performance & longevity. Even though the TTR125L is air-cooled – unlike most liquid-cooled motocross bikes – it still requires periodic inspection of its smaller cooling system, which includes coolant for the thermostat and overflow system. Here's a MotoSport.com proprietary step-by-step guide for properly changing and maintaining your TTR125L coolant:

Preparation

  • Safety first: Make sure the bike is on level ground, the engine is completely cool, and you have gloves and safety glasses.
  • Gather supplies: Fresh coolant (manufacturer-recommended, ethylene glycol-based), a drain pan, a funnel, and distilled water if flushing.

Draining the Old Coolant

  • Start by removing the seat and side covers to access the thermostat assembly.
  • Place a drain pan under the drain bolt, typically found at the base of the thermostat housing (referenced in your owner's manual).
  • Carefully loosen the drain bolt – coolant will begin to flow out, so let it drain completely.
  • Remove the radiator cap or the thermostat cover to accelerate draining.

Optional: Flushing the System

  • Fill the system with a 50/50 mix of distilled water and vinegar to remove buildup, and briefly run the engine until warm, then drain completely.
  • Repeat flush with only distilled water to clear out vinegar; drain again until empty.

Refilling with Fresh Coolant

  • Ensure the drain bolt is replaced with a new sealing washer, and torque to specification.
  • Using a funnel, slowly add fresh coolant up to the bottom of the thermostat filler neck, pausing if air gurgles out – rock the bike gently to help release trapped air.
  • Once full, briefly start the bike with the filler cap off and let it idle for a minute to release remaining air pockets. You may see the coolant level drop – top off as needed.
  • Replace all covers and the radiator or thermostat cap securely.
  • Fill the overflow reservoir up to the full line, if equipped.

Checking Levels and Final Steps

  • After riding and the bike cools to room temperature, check coolant level in both the thermostat and the reservoir – top off as needed.
  • Inspect for any leaks around the thermostat, hoses, or drain bolt.
  • Always dispose of old coolant properly at a recycling center.

TTR125L-Specific Notes

  • Air-cooled system: While most of the 2018 TTR125L's cooling is handled by air, the bike still features a minimal liquid system for temperature regulation, so coolant changes are less frequent but still necessary for optimal engine health.
  • Coolant capacity: Always check your exact model's specification to avoid under- or over-filling. The TTR125L uses significantly less coolant compared to full-size liquid-cooled bikes.
  • Gasket care: When removing the thermostat cover, check gaskets and O-rings for wear – replace if needed to prevent leaks.

Proper coolant maintenance protects your TTR125L from overheating, extends engine life, and keeps you riding longer. Every component you need for your coolant change is available at MotoSport – make it easy, do it right, and ride safe.

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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.