How to Change the Coolant in a 1996 Cobra BM50

Shop parts for a 1996 Cobra BM50 Dirt Bike.

Routine coolant changes help keep your 1996 Cobra BM50 running cool and extend the engine life—especially since high-performance 2-stroke dirt bikes like the BM50 operate at higher RPMs and temperatures, commonly under race conditions. This step-by-step guide from MotoSport provides a robust and proprietary process for draining, flushing, and refilling the cooling system, plus crucial ownership tips unique to this classic mini motocrosser.

Things to Know About the 1996 Cobra BM50

  • Specialized cooling needs: The BM50's compact, high-revving engine makes proper coolant circulation and air-purging vital to prevent hot spots and engine damage.
  • Sensitive aluminum alloys: Only use motorcycle-specific coolants compatible with aluminum. Avoid automotive antifreeze with silicates that may erode soft metal components.
  • Access points: The BM50 offers straightforward access to the radiator and drain bolt but has tight spaces, so small tools are helpful.

What You'll Need

  • Fresh, motorcycle-specific premixed coolant (OR concentrated + distilled water)
  • 4 mm or 5 mm Allen wrench (check your drain bolt size)
  • Small funnel
  • Catch pan for old coolant
  • Shop rags
  • Torque wrench (optional, for correct drain bolt refit)
  • Safety gloves & eye protection

Step 1: Prepare the Cobra BM50

  • Set the bike upright on a stand, engine completely cool.
  • Remove the radiator cap.
    Tip: Loosen any shrouds or plastic that block access. Be careful of delicate radiator fins.
  • Position your catch pan beneath the engine, lining the area with rags to catch spills.

Step 2: Drain Old Coolant

  • Locate the coolant drain bolt on the water pump (usually left or right side engine case).
  • Slowly loosen the bolt–some models may also have a small copper crush washer that should be replaced if worn.
  • Let coolant fully drain. If your BM50 lacks a dedicated drain bolt, slowly loosen the lowest radiator hose clamp and let the hose hang free.

Step 3: Flush the Cooling System (Optional but Recommended)

  • Reinstall the drain bolt (finger-tight).
  • Fill the radiator with distilled water.
  • Reinstall the radiator cap and start the engine for 1-2 minutes, just long enough to circulate water. Do not let the engine overheat.
  • Shut off engine, let cool completely, then drain the system again.
  • For heavily scaled systems, repeat with a 50/50 distilled water and vinegar flush, then rinse with distilled water.

Step 4: Add New Coolant

  • With the drain bolt and washer torqued to spec, place a funnel in the radiator fill neck.
  • Slowly pour fresh coolant until the radiator is full, giving time for trapped air bubbles to escape.
  • With the cap still off, briefly tilt the bike from side to side to help purge more air.
  • Top off again if the level drops.

Step 5: Bleed the System & Final Checks

  • Start the engine and let it idle with the radiator cap off for 1-2 minutes. Watch for bubbles as trapped air exits.
  • When bubbles stop rising and the coolant level stabilizes, reinstall the radiator cap securely.
  • Wipe away any spills and check all hose clamps for tightness.
  • After a short ride, let the engine cool, recheck the coolant level, and top off as needed.

Maintenance Tips for Longevity

  • Replace coolant at least every 2 years–or more often if racing or riding hard.
  • Check for leaks around the water pump, hoses, and radiator after every coolant change.
  • Keep the radiator fins clean and free of debris for maximum cooling efficiency.

Keeping your 1996 Cobra BM50's cooling system fresh and air-free is crucial for high-revving, reliable performance. Use only coolants safe for small-displacement, aluminum-constructed motocross engines–and don't forget, if you need gaskets, hoses, or a new radiator cap, Shop parts for a 1996 Cobra BM50 Dirt Bike.

Related Shopping Categories

Shop Radiators for a 1996 Cobra BM50 Dirt Bike.

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Shop Temperature Sensors for a 1996 Cobra BM50 Dirt Bike.

Shop Tools for a 1996 Cobra BM50 Dirt Bike.

Shop Radiator Hoses for a 1996 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.