How to Change the Coolant in a 1995 Cobra BM50: MotoSport Proprietary Guide

Shop parts for a 1995 Cobra BM50 Dirt Bike.

Routine coolant replacement is crucial to keep your 1995 Cobra BM50 performing its best, prevent overheating, and protect engine internals. The BM50, known for its competitive performance in the youth mini class, has a compact cooling system – correct service ensures reliability and longevity.

Preparation and Safety

  • Let the bike cool down completely before starting to avoid burns.
  • Have a suitable drain pan for old coolant. Dispose of used coolant at a proper facility – never pour down drains or on the ground.
  • Gather tools: flat screwdriver, pliers, clean rags, fresh coolant (Cobra recommends a high-quality racing coolant for best thermal transfer).

Draining the Old Coolant

  • Remove the radiator cap for pressure release.
  • Locate and loosen the lower radiator hose clamp, then slide the hose off the radiator fitting to allow coolant to fully drain into your pan. Optionally, tip the bike gently side-to-side for complete emptying.
  • Inspect the drained coolant for excess debris or discoloration — this can indicate internal corrosion or failure.

Flushing the Cooling System

For best maintenance, it is advised to perform a simple flush:

  • Reconnect the lower radiator hose.
  • Fill the radiator with clean distilled water.
  • Start your BM50 and run for a minute. Shut off, let cool, then drain again.
  • Repeat this process two more times for a thorough rinse.

Filling with New Coolant

  • Reconnect hoses securely and check clamps for tightness.
  • Fill the radiator slowly until near the top. The BM50's cooling circuit holds approximately 450–500 milliliters — never overfill.
  • Check for air pockets: Rock the bike gently as you fill, and pause periodically to let trapped air escape.
  • Some BM50s may have a small bleed bolt near the radiator or cylinder — crack it open briefly until coolant dribbles out, then retighten.

Burping & Cycling the System

  • Leave the radiator cap off. Start the bike and let it idle for one minute.
  • Watch for bubbling; top up the radiator as air escapes and the coolant level drops.
  • Once no more bubbles emerge and the level stabilizes, stop the engine and refit the radiator cap securely.

Final Checks

  • Clean up any spills and carefully inspect all hoses and connections for leaks.
  • Run your BM50 one last time, monitoring for rapid temperature gain or leaks around the radiator cap and hose clamps.
  • Check the coolant level once cool, topping up as needed to ensure proper volume.

Special Considerations for the 1995 Cobra BM50

  • Use a premium, lightweight racing coolant for optimal temperature stability. Avoid straight water; some wetting agent is beneficial – the BM50's small cylinder and precision water jackets depend on high heat transfer.
  • Regularly inspect the small impeller: This is a common wear point and a known issue on older BM50s. Damage here impedes coolant flow and risks overheating, especially in race conditions.*
  • Always record service intervals for your Cobra – reliability in youth MX depends on strict maintenance.

* Refer to your Cobra owner's manual for specific impeller service procedures. The BM50's compact engine is particularly sensitive to coolant flow restrictions.

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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.