How to Change the Coolant in a 1999 Cobra BM50: Essential Guide for Owners
Shop parts for a 1999 Cobra BM50 Dirt Bike.
Changing the coolant in your 1999 Cobra BM50 is a vital maintenance step that keeps your engine running cool and protected. This youth race bike features a liquid-cooled, single-cylinder two-stroke engine, and regular coolant changes are especially important to prevent overheating – the BM50 runs hot under heavy use. Follow this exclusive MotoSport guide to completely flush and refill the cooling system with precision and confidence.
Why Coolant Maintenance Matters on the Cobra BM50
- Performance: Clean, fresh coolant prevents dangerous overheating, which can lead to engine seizure or premature wear.
- Longevity: Old or contaminated coolant increases corrosion risk inside the aluminum radiator and engine, shortening component life.
- Consistency: Proper coolant levels keep temperature stable, crucial for a high-revving two-stroke mini-moto like the BM50.
Before You Begin
- Only use high-quality coolant and distilled water to avoid mineral buildup or corrosion.
- Tools Needed: Screwdrivers, pliers, rags, drain container, funnel, safety gloves, and eye protection.
- Work on a cool engine. Allow the BM50 to sit until the radiators and hoses are safe to touch.
Step-by-Step Coolant Change Process
-
Remove the Bodywork:
Take off the seat and side panels as needed for unobstructed access to the radiators and hoses. -
Locate the Radiator Cap & Drain Point:
The BM50's radiator cap is usually on top of the left-side radiator. The lowest coolant hose or the water pump cover will serve as the drain.
Tip: Place your drain pan directly under the lowest point. -
Drain the Old Coolant:
Remove the radiator cap first to release pressure. Next, loosen the drain bolt on the water pump cover and/or disconnect the lowest radiator hose.
Allow all coolant to empty into the pan. -
Flush with Distilled Water (Recommended):
Replace the hose and secure the drain bolt. Fill the system with distilled water, reinstall the cap, and briefly run the engine (<30 seconds) to circulate.
Shut off and drain again. Repeat until the water runs clear. -
Refill with Fresh Coolant:
Secure all connections. Using a funnel, slowly add coolant (usually 450-500mL for the BM50, but verify in your manual). Fill to just below the filler neck.
Note: Only use coolants compatible with aluminum engines and radiators. -
Bleed Air from the System:
Gently rock the bike side-to-side, compress hoses by hand, and open the small bleed/return hose at the top of the radiator (if equipped) until bubbles stop and steady coolant emerges. -
Check for Leaks & Top Off:
Reinstall the cap. Start the bike and let it idle until warm; the coolant will circulate, and any air will purge into the reservoir or bleed back through the system. Shut down, allow to cool, then recheck and top off coolant if needed. -
Clean Up & Dispose Properly:
Wipe spilled coolant from the bike. Dispose of old coolant responsibly—never pour down drains.
Special Considerations for the 1999 Cobra BM50
- Small capacity: The BM50 radiator has a very low fill volume, so do not overfill. Watch the level closely when topping up.
- Racing duty: This model is built for hard use. After any overheating event, always inspect for contamination in the coolant and repeat the flush if necessary.
- Aluminum construction: Only use silicate-free, aluminum-safe coolants made specifically for motocross/motorcycle engines.
- Inspect hose clamps, radiator mounts, and the water pump weep hole for leaks. Replace worn parts to prevent trackside breakdowns.
Your 1999 Cobra BM50 is a true race machine – regular coolant changes are the simplest way to protect its power and durability for every moto.
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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.