How to Change the Coolant in a 1999 Cobra CM50: A MotoSport.com Exclusive Guide
Shop parts for a 1999 Cobra CM50 Dirt Bike.
Keeping your 1999 Cobra CM50 running cool is critical to performance and engine longevity, especially in a two-stroke mini machine designed for spirited youth racing. This guide details the proprietary MotoSport process for a complete and confident coolant change, with special notes unique to the CM50 that every owner must know.
What Makes the Cobra CM50 Unique?
The 1999 Cobra CM50 is a championship-winning, two-stroke 50cc motocross bike built for high revs and rapid starts. Its cooling system is simple but high-performing, with a compact radiator and water pump designed for aggressive riding. Always use coolants designed for aluminum engines and never mix coolant types. Factory tolerances are tight on this model, so maintaining a bubble-free, sediment-free system keeps the engine safe from overheating and costly cylinder wear.
Step-by-Step: Changing the Coolant on Your Cobra CM50
- Cool and Prepare
Let the engine cool completely before starting. Place your Cobra CM50 on a stable, upright stand in a well-ventilated area. Remove the seat and side panels for easier access if needed. - Drain the Old Coolant
Locate the radiator drain bolt or, if your model uses a lower hose design, loosen the lower radiator hose clamp where the hose connects to the engine. Place a drain pan underneath. Remove the radiator cap to allow air in – this speeds up draining. Allow all coolant to completely empty out. - Flush the System (Recommended)
Reattach the hose or drain bolt. Fill the radiator with distilled water (never tap water – minerals can damage your system). Run the engine for a minute, shut it off, and drain again. Repeat until the water runs clean. - Fill With Fresh Coolant
Using a funnel, slowly pour in high-quality, pre-mixed 50/50 coolant for aluminum engines. Fill up to the base of the radiator filler neck. - Bleed the System
Start the engine with the radiator cap off and let it idle. Gently rock the bike from side to side – this encourages trapped air bubbles to escape ("burping" the system). When the coolant level drops, top it off. Once no more bubbles appear and coolant stays topped up, shut off the engine and reinstall the radiator cap securely. - Check and Top off the Reservoir
If your CM50 is fitted with a coolant overflow reservoir, ensure it is filled between MIN and MAX lines after the engine cools down completely. - Dispose of Old Coolant Properly
Never pour used coolant down the drain. Bring it to an auto parts store or a local hazardous waste center for safe disposal.
Important Notes Specific to the Cobra CM50
- Avoid air pockets: This model's small coolant passages make air pockets especially dangerous, leading to rapid overheating and seizure if not fully bled. Take your time during the fill and burp stages.
- Inspect hoses and rad cap: The CM50's hoses and cap are often exposed to impacts and vibration. Replace if they show any signs of cracking, softness, or leaks.
- Choose the right coolant: Only use coolants compatible with high-revving two-stroke engines and aluminum radiators. Avoid any that contain silicates or phosphates.
Last Check
After your first ride, allow the engine to cool, then re-check the radiator and reserve tank levels. Top off as needed; minor loss after the first heat cycle is normal as the system purges any remaining air.
This method ensures your 1999 Cobra CM50's cooling system is reliable for the tightest race or longest ride. Stay on top of maintenance for maximum performance.
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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.