How to Change the Coolant in a 2002 Cobra BM50: A MotoSport.com Proprietary Guide

Shop parts for a 2002 Cobra BM50 Dirt Bike.

Changing the coolant in your 2002 Cobra BM50 is an essential part of keeping the bike running cool and maximizing engine life. This mini motocross racer features a compact liquid cooling system designed for high-revving performance, meaning correct coolant change and air removal is even more important than with larger bikes. The proprietary MotoSport.com process below ensures your Cobra BM50 is properly maintained and competition-ready.

What You'll Need

  • Pre-mixed motorcycle coolant (or coolant concentrate plus distilled water)
  • Catch pan
  • Funnel
  • Rags or towels
  • Socket set/Phillips driver (to remove panels and drain plug)
  • Protective gloves and eyewear

Step 1 – Access the Radiator and Drain the Coolant

  • Allow the engine to cool completely before starting.
  • Remove the seat and side panels to access the radiator and hoses. Locate the radiator cap and lower drain bolt or drain hose (typically at the bottom of the radiator).
  • Place your catch pan under the radiator. Slowly loosen and remove the radiator cap to prevent sudden spills (this also relieves any system pressure).
  • Remove the drain bolt or loosen the drain hose clamp. Allow all old coolant to drain completely. Dispose of it responsibly—never pour it down a drain or onto the ground.

Step 2 – Flush (Optional, Highly Recommended)

  • For a thorough flush, fill the system with distilled water after draining the coolant. Run the engine on low throttle for about 1 minute, then let it cool and drain again.
  • Repeat this flush procedure if the water looks cloudy or colored, indicating leftover old coolant or debris.

Step 3 – Refill with Fresh Coolant

  • Verify your coolant—the Cobra BM50 typically uses 450-500 ml. If using concentrate, mix it 50/50 with distilled water before adding.
  • With the drain bolt reinstalled and snug, slowly pour coolant into the radiator using a funnel. Allow air to escape as you go. Fill gradually until it's just below the filler neck.
  • Check for leaks at the drain bolt and hose connections before proceeding.

Step 4 – Bleed the Cooling System

  • To bleed trapped air, gently squeeze the return hose at the back of the radiator or loosen it slightly until air bubbles are visible and coolant flows steadily. Secure the hose after.
  • It's recommended to "burp" the system by briefly starting the bike with the radiator cap off, letting it idle, and gently rocking the bike to free trapped air. Stop as soon as you see coolant rise toward the neck or bubbling subsides.
  • Refill the radiator as needed to top off. Replace the radiator cap firmly once the level is correct.

Step 5 – Final Inspection

  • Start the engine and let it idle for a few minutes, watching for any leaks and monitoring the coolant level after the first heat cycle.
  • Allow the bike to cool completely, then recheck and top up the coolant if necessary.
  • Reinstall any panels and the seat.

Special Notes for 2002 Cobra BM50 Owners

  • This bike's compact cooling system is high-strung for maximum performance. Even small air bubbles left in the system can cause overheating or inconsistent performance–be thorough in the bleeding and burping process.
  • Always use high-quality motorcycle coolant, never automotive anti-freeze, as the wrong type can damage seals and internal components.
  • Factory spec calls for 450-500 ml of coolant. Overfilling can cause overflow; underfilling can cause overheating.
  • Inspect hoses and clamps for any signs of wear, swelling, or cracking while you have access–these should be replaced if damaged for reliable operation.

Routine coolant changes keep your Cobra BM50 running at its peak & protect your investment. Staying on top of this basic maintenance is the best way to ensure you're always ready for moto action.

Related Shopping Categories

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Shop Temperature Sensors for a 2002 Cobra BM50 Dirt Bike.

Shop Tools for a 2002 Cobra BM50 Dirt Bike.

Shop Radiator Hoses for a 2002 Cobra BM50 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.