How to Change the Coolant in a 2004 Honda CR85 Big Wheel

Shop parts for a 2004 Honda CR85RB Dirt Bike.

Regular cooling system maintenance is essential for peak performance in your 2004 Honda CR85RB Big Wheel. Changing the coolant prevents overheating and protects your two-stroke engine from internal corrosion. Here's a step-by-step guide specific to your MMY (Make/Model/Year) dirt bike–including notable model-specific tips.

What You'll Need

  • Genuine Honda or equivalent coolant (preferably pre-mixed for aluminum engines)
  • Drain pan
  • 10mm wrench or socket
  • Flathead screwdriver
  • Funnel
  • Clean shop towels
  • Protective gloves and eye protection

Preparation

  • Ensure the bike is cold before starting. Pressure in the cooling system drops as it cools, reducing burn risk.
  • Work in a well-ventilated area, away from sparks or open flames.
  • Prop the bike on a stable stand, keeping it as level as possible.

Drain the Old Coolant

  • Remove the radiator cap on the left side of the bike using a flathead screwdriver. This releases internal pressure and helps coolant drain freely.
  • Locate the coolant drain bolt situated at the lower water pump cover on the right side of the engine (typically a 10mm bolt).
  • Position your drain pan underneath and loosen the drain bolt. Allow all coolant to drain completely.
  • Inspect the drain bolt washer (crush washer) and replace if damaged to prevent leaks on reinstallation.
  • Retighten the drain bolt securely after the coolant has stopped dripping out.

Flush the System (Recommended)

  • If the coolant is severely discolored or if your bike has overheated in the past, fill the radiator with distilled water after draining.
  • With the drain bolt reinstalled, start the engine for 1-2 minutes with the radiator cap off to circulate the water and dislodge old residue.
  • Repeat the drain step to remove flushing water. Don't let the engine get hot during this process.

Refill with Fresh Coolant

  • Use a funnel to slowly pour new coolant into the radiator.
  • Pause intermittently and gently rock the bike side to side to help trapped air escape.
  • Fill to just below the radiator neck.
  • If your CR85RB is equipped with a coolant overflow tank, fill it to the "Full" line as indicated on the reservoir.

Bleed Air from the System

  • With the cap off, start the engine and let it idle for 1-2 minutes. Blip the throttle to encourage air bubbles to rise and escape.
  • Check fluid level again–top off if needed.
  • Once the coolant level stabilizes with no more bubbles, install the radiator cap securely.

Final Checks & Disposal

  • After one short ride, let the engine cool and recheck the levels in both the radiator and overflow tank. Top off if necessary.
  • Make sure to properly recycle old coolant at an approved recycling center. Never pour it down drains or onto the ground.

Model-Specific Tips for the 2004 Honda CR85RB Big Wheel

  • The CR85RB (Big Wheel) shares its cooling system with the CR85R but features a larger wheel and taller stance. The radiator and water pump placement are identical, but bigger wheels make access slightly easier, especially when working on a stand.
  • Always use coolant specified for aluminum radiators to protect internal passages. Honda GN4 or equivalent silicate-free formula is recommended.
  • Inspect cooling hoses for cracks or leaks–the CR85RB's high-revving two-stroke engine puts extra stress on seals and joints during race use.

Keep your 2004 CR85RB running cool and crisp by following these steps every season or after intense races. Timely coolant changes are one of the simplest ways to ensure long engine life and top-notch performance.

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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.