How to change the coolant in a 2005 Honda CR85 Big Wheel Dirt Bike

How to Change the Coolant in a 2005 Honda CR85 Big Wheel

Shop parts for a 2005 Honda CR85RB Dirt Bike.

Proper cooling is crucial for your 2005 Honda CR85RB (Big Wheel) – a machine known for its high-revving two-stroke performance and lightweight build. Whether you're prepping for race day or routine maintenance, changing the coolant is a straightforward job that helps prevent overheating and safeguards your engine from corrosion. Follow this exclusive MotoSport guide for the best results on this expert-level minibike.

What You'll Need

• High-quality, ethylene glycol-based coolant with corrosion inhibitors
• Coolant catch pan
• 8mm socket or wrench
• Funnel
• Shop towels
• Safety gloves and goggles
• New water pump drain bolt washer (recommended but optional)

Step 1: Prep the Bike

• Work with the engine cold to prevent burns from hot coolant or steam.
• Place your CR85RB upright on a stand in a well-ventilated area.
• Remove the radiator cap slowly to relieve internal pressure.

Step 2: Drain the Old Coolant

• Locate the coolant drain bolt – typically on the water pump cover on the right side of the engine (it may have a copper or aluminum washer).
• Position the catch pan below the bolt.
• Remove the bolt and allow all coolant to drain out. To speed up draining, you can gently rock the bike side-to-side.
• Inspect the old washer and replace it if necessary for a leak-free seal at reassembly.

Step 3: Flush the System (Optional but Recommended)

• For optimal system health, you can refill with distilled water, run the engine briefly (without overheating), then drain again to remove lingering contaminants.
• Repeat as needed until the water runs clear.

Step 4: Reinstall the Drain Bolt

• Clean the area and threads.
• Install a fresh washer if you have one.
• Tighten the drain bolt securely, but do not overtighten (refer to your model's service torque specification for safety – typically around 9 lb-ft, but confirm for your exact model).

Step 5: Add New Coolant

• Place a funnel into the radiator neck.
• Slowly pour in the new ethylene glycol-based coolant – only use types recommended for aluminum radiators with corrosion inhibitors.
• Fill to the bottom of the filler neck, allowing bubbles to escape.

Step 6: Bleed Air from the System

• Start the bike according to standard procedure and let it idle for a few minutes with the radiator cap off to help air escape. Never let the engine overheat.
• You may see the coolant level drop as air bleeds out—top off as needed.
• Once no visible bubbles remain, shut off the bike, and reinstall the radiator cap securely.

Step 7: Check for Leaks & Proper Fill

• Inspect the drain and hoses for leaks.
• After a short ride, double-check coolant level and top off if necessary.

CR85 Big Wheel (85RB) Owner Notes

• The CR85RB features larger wheels and higher ground clearance than the standard CR85R, but the cooling system is otherwise unchanged between models.
• Only use ethylene glycol-based coolant – alternatives can damage your aluminum radiator and water pump components.
• Honda recommends checking coolant every two rides and changing it every two years or more often in extreme racing conditions.
• Dispose of used coolant responsibly – never pour it down the drain as it is toxic to people and animals.

Final Tips

• Tighten all bolts to factory specification.
• Always monitor engine temperature after a coolant change, especially in hot weather or during slow riding.
• If you notice persistent leaks or overheating, inspect the radiator hoses, cap, and water pump carefully before riding again.

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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.