How to Change the Coolant in a 2003 Honda CR85 Big Wheel

Shop parts for a 2003 Honda CR85RB Dirt Bike.

The 2003 Honda CR85 Big Wheel (CR85RB) is a high-revving, performance-oriented two-stroke race bike designed for youth riders who need excellent cooling to keep up with demanding track conditions. Regularly changing the coolant is essential to prevent overheating and extend engine life. Follow this guide for a complete coolant replacement, tailored for your CR85RB, including tips specific to this model.

What You Need

  • High-quality ethylene glycol-based coolant with corrosion inhibitors – always use a coolant suitable for aluminum radiators to prevent premature wear.
  • Drain pan
  • 10mm socket or wrench
  • New water pump crush washer (Honda part number 90463-ML7-000 is recommended)
  • Clean funnel
  • Gloves and protective eyewear
  • Distilled water (optional for flushing)

Preparation

  • Ensure the engine is completely cool before starting to avoid burns and pressurized coolant sprays.
  • Work in a well-ventilated area and take care to avoid flames or sparks near the coolant and fuel system.
  • Safely prop your bike on a stand.

Step-by-Step Coolant Change for the CR85 Big Wheel

  1. Remove the radiator cap: Slowly turn and remove the radiator cap on the left side of the bike. Never open when hot.
  2. Locate and remove the coolant drain bolt: The drain bolt is found on the water pump cover, usually near the bottom right side of the engine. Place a drain pan under the bolt, then use a 10mm wrench to remove it. The coolant will flow out – allow it to fully drain.
    Tip: After main drainage, you can give the kickstarter a few slow kicks (kill switch off) to help push remaining coolant from the system.
  3. Inspect and replace the crush washer: Each coolant change on the CR85RB should include a new water pump cover crush washer to ensure a leak-proof seal when reinstalling the drain bolt.
  4. Optional: Flush the system (recommended for old or discolored coolant): Reinstall the drain bolt with the new washer and fill the radiator with distilled water. Start the bike and let it idle briefly, then shut off and repeat the drain procedure. This extra step helps remove any lingering debris or residue.
  5. Reinstall the drain bolt: Tighten the drain bolt to manufacturer torque specifications, taking care not to overtighten and damage threads.
  6. Refill with fresh coolant: Slowly pour in new coolant until the radiator is filled to the base of the filler neck. If your CR85RB uses an expansion tank, fill it to the indicated mark as well. Avoid air pockets by gently rocking the bike side-to-side.
  7. Bleed air from the system: Start the engine and let it idle for several minutes with the radiator cap off. Watch for rising air bubbles; add more coolant if the level drops. Once bubbling stops and the fluid level stabilizes, turn off the engine, top up if necessary, and secure the radiator cap.
  8. Check for leaks: Carefully inspect around the water pump cover and drain bolt. Address any leaks before riding.

Model-Specific Notes for 2003 CR85 Big Wheel Owners

  • This model features aluminum radiators, which require only ethylene glycol-based coolant designed for aluminum – avoid coolant for automobiles with silicates, as they can cause premature radiator and water pump wear.
  • CH85RB (Big Wheel) runs hotter under competition loads – inspect the radiator and hoses for debris or pinched lines during each coolant change.
  • The CR85RB water pump is especially sensitive to leaks from improper crush washer installation or over-tightened bolts. Always inspect and replace the washer with each service.
  • Coolant should be changed every 40–50 hours of riding or annually, whichever comes first, to ensure peak system performance.

Disposal & Safety Tips

  • Never pour used coolant on the ground or in storm drains. Always recycle in accordance with local regulations.
  • Coolant is highly toxic to pets and wildlife. Store new and used coolant out of reach of children and animals.

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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.