How to Change the Coolant in a 2021 Yamaha YZ85: MotoSport Guide

Shop parts for a 2021 Yamaha YZ85 Dirt Bike.

Regular maintenance keeps your 2021 Yamaha YZ85 running at its best–and changing the coolant is crucial for peak performance, engine longevity, and preventing overheating. This proprietary MotoSport guide walks you step-by-step through the coolant change, including notes unique to this iconic two-stroke mini motocross machine.

Before You Begin

  • Ensure the engine is completely cool to avoid burns and pressure spray.
  • Work on a stable, level surface with ample lighting and access to both sides of the bike.
  • Have on hand: correct capacity of dirt bike coolant, distilled water (if flushing), catch pan, socket/ratchet for drain bolt, funnel, clean rag, and new drain bolt gasket (recommended).

Step 1: Locate and Access the Cooling System

  • The radiator cap is on top of the left-side radiator. Remove the front number plate if easier access is needed.
  • Locate the drain bolt–typically on the lower water pump cover at the engine’s right side.
  • Place a drain pan securely beneath the drain bolt to capture all old coolant.

Step 2: Drain the Old Coolant

  • Remove the radiator cap to relieve pressure.
  • Using a socket, carefully loosen and remove the coolant drain bolt.
  • Allow the coolant to fully drain into your catch pan. Lean the bike gently to both sides if necessary, but not far enough to spill or create a hazard.

Step 3: Flush (Optional but Recommended)

  • If switching coolant types, or for thorough maintenance, flush the system by filling with distilled water (never tap water) and draining again until it runs clear.
  • For stubborn residues, you may repeat the flush process. Ensure all water drains fully to avoid dilution.

Step 4: Reinstall Drain Bolt

  • Inspect the drain bolt and replace its gasket if it shows damage or wear.
  • Thread in and torque the bolt to the manufacturer’s specification–do not overtighten.

Step 5: Fill with New Coolant

  • Using a funnel, slowly pour in the new coolant up to the specified level in the radiator filler neck.
  • Do not mix coolants–stick with a type compatible with aluminum radiators and recommended for your Yamaha YZ85.

Step 6: Bleed Air from the System

  • With the radiator cap off, gently tilt the bike side-to-side to help air bubbles escape.
  • Start the engine and let it idle for just a minute. Shut off and top off coolant as necessary–add slowly to prevent overflow.

Step 7: Check and Recheck

  • Install and tighten the radiator cap.
  • Wipe away any coolant spills and check for leaks at the drain bolt and hose junctions.
  • After a short ride, let the bike cool and recheck the coolant level–top up if needed.

YZ85-Specific Notes

  • The 2021 YZ85 uses a relatively small coolant volume due to its compact, race-bred engine. Track regular coolant level before every ride–hard riding and track debris can accelerate fluid consumption or loss.
  • Inspect radiator and hoses for damage after tip overs or crashes, as these lightweight components can be more vulnerable on youth and race bikes.
  • Recommended intervals: Yamaha advises a complete coolant change annually or at severe service intervals, whichever comes first. Replace sooner if the coolant appears contaminated, discolored, or diluted.

Regularly changing your YZ85’s coolant protects against corrosion, overheating, and unexpected breakdowns, keeping you on the track and out of the pits.

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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.