How to Change the Coolant in a 2006 Honda CR85 Big Wheel

Shop parts for a 2006 Honda CR85RB Dirt Bike.

The 2006 Honda CR85RB Big Wheel is a competition-ready mini dirt bike designed for young riders stepping into bigger tracks. Regular maintenance is essential to keep the CR85RB's high-revving two-stroke engine running cool and strong. Changing the coolant at least once per riding season, or every 40–50 hours, is recommended to prevent overheating and keep your engine components protected.

What You Need

  • Fresh engine coolant (Honda HP or a recommended equivalent compatible with aluminum radiators)
  • 14mm socket or wrench
  • Large flathead screwdriver
  • Drain pan
  • Funnel
  • Gloves and safety glasses
  • New crush washer (optional but recommended for drain bolt)
  • Clean water (for flushing)—optional but ideal

Step-by-Step Coolant Change Process

  1. Let the Bike Cool Completely
    Always work on the cooling system when the engine is cold. Opening the radiator cap on a hot bike can cause pressurized steam and fluid to spray, risking burns.
  2. Remove the Seat and Shrouds (If Needed)
    For better access to the radiator cap and tank, you may need to remove the seat and the right side panel. On the CR85RB, this often provides a clearer view and access.
  3. Open the Radiator Cap
    Slowly loosen the radiator cap using a flathead screwdriver or by hand, allowing any residual pressure to escape.
  4. Find & Remove the Coolant Drain Bolt
    Position your drain pan under the water pump cover, which is on the right-hand side of the engine. The coolant drain bolt is typically the lower bolt with a copper washer–14mm size. Remove this bolt, allowing the old coolant to drain into the pan. If your CR85RB has an additional drain on the cylinder, remove it as well.
    For best results, tilt the bike slightly side-to-side to empty as much coolant as possible.
  5. Flush the System (Optional for Thoroughness)
    Reinstall the drain bolt, then fill the radiator with clean distilled water. Replace the cap, start the engine, and let it idle for a minute. Shut off, allow it to cool, and drain again. Repeat this step until the water runs clear.
  6. Reinstall the Drain Bolt
    Inspect the copper crush washer; replace it if worn. Reinstall and tighten the drain bolt securely, but do not overtighten.
  7. Add Fresh Coolant
    Using a funnel, fill the radiator up to the filler neck. Gently rock the bike side-to-side to release trapped air. Top off as needed until the level remains steady at the neck.
  8. Bleed the Cooling System
    With the radiator cap off, start the engine and let it idle for a minute. Watch for air bubbles exiting the filler neck–this helps purge the system. Shut off the engine, check the coolant level, and top off again if required.
  9. Replace the Radiator Cap
    Install the cap firmly. Wipe any spilled coolant from the bike.
  10. Recycle Old Coolant Responsibly
    Used coolant is toxic–always dispose of it at a proper recycling center or hazardous waste facility.

Key Things CR85RB Owners Should Know

  • The CR85RB Big Wheel features larger wheels than the standard CR85R, improving stability for bigger or more advanced riders. Coolant procedures are nearly identical with no special tools required.
  • Always use a coolant safe for aluminum components. Some automotive coolants may not provide the required corrosion inhibitors; stick with Honda's formula or a high-quality motorcycle coolant.
  • Check radiator hoses and clamps for leaks while servicing. Replace any brittle or cracked hoses right away to prevent trail-side breakdowns.
  • The radiator capacity is approximately 0.57 quarts (0.54 liters).
  • If riding in hot conditions or racing, monitor your coolant level frequently–two-strokes tend to run hotter under aggressive riding.

Routine Maintenance Matters

Replacing your coolant regularly helps prevent internal corrosion, overheating, and costly repairs–especially vital for high-revving two-strokes like the 2006 Honda CR85 Big Wheel. If you notice frequent overheating, steam from the radiator, or random coolant loss, inspect all system parts for leaks or damage and address them before your next ride.

Related Shopping Categories

Shop Radiators for a 2006 Honda CR85RB Dirt Bike.

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Shop Temperature Sensors for a 2006 Honda CR85RB Dirt Bike.

Shop Tools for a 2006 Honda CR85RB Dirt Bike.

Shop Radiator Hoses for a 2006 Honda CR85RB Dirt Bike.

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.