How to Change the Coolant in a 2025 Yamaha YZ125

Shop parts for a 2025 Yamaha YZ125 Dirt Bike.

Keeping your 2025 Yamaha YZ125 performing at its best means routine maintenance–and changing the coolant is crucial for protecting your engine from overheating and corrosion. Properly servicing the cooling system ensures consistent power delivery on the track or trail.

Tools & Supplies Needed

  • Container for old coolant
  • Socket wrench set
  • Fresh coolant: Ethylene glycol-based, aluminum-safe, pre-mix or mix 50% coolant with 50% distilled water
  • Replacement copper washer (recommended)
  • Gloves & shop rags

Step-by-Step Coolant Change Procedure

  1. Let the engine cool completely before servicing–removing the radiator cap when hot can cause injuries from steam or boiling coolant.
  2. Position your YZ125 upright on a stand and place a drain pan under the engine.
  3. Remove the radiator cap to allow the system to vent.
  4. Locate and remove the coolant drain bolt at the bottom of the water pump area. Let all old coolant drain out. (Check your manual for precise bolt location.)
  5. Inspect and clean the copper washer, replacing it if worn or damaged. Reinstall the drain bolt and torque it to 10 Nm (7.2 ft–lb).
  6. Pour fresh coolant slowly into the radiator up to the specified level. The system capacity is 0.95 L (1.00 US qt).
  7. With the bike upright, gently squeeze the radiator hoses to help remove any air bubbles.
  8. Replace the radiator cap securely.
  9. Start the engine and let it idle for a few minutes with the radiator cap on to circulate the coolant and purge remaining air. Shut off and re-check coolant level once cool. Top off as necessary.

YZ125 Model-Specific Tips

  • Use a high-quality coolant designed for aluminum engines to prevent corrosion and overheating.
  • The 2025 YZ125's lightweight, liquid-cooled two-stroke design requires optimal thermal management for best throttle response and longevity.
  • Inspect both radiators for mud, debris, or damage each time you perform a coolant change.
  • Monitor coolant levels before every ride–low coolant can result in rapid engine overheating, especially during aggressive riding.

When to Change Coolant

  • At least once every season, or more frequently after muddy or wet riding conditions.
  • If you notice discolored or cloudy coolant, overheating, or after a rebuild.

Regular coolant service is a simple way to safeguard your 2025 Yamaha YZ125’s legendary engine performance and keep you on the podium longer.

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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.