How to Change the Coolant in a 1998 Cobra BM50 – Complete Guide
Shop parts for a 1998 Cobra BM50 Dirt Bike.
Changing the coolant in your 1998 Cobra BM50 is a straightforward maintenance task that helps keep your mini motocross bike running cool and performing at its best. This model, known for its high-revving 2-stroke engine and competitive focus, benefits from a well-maintained cooling system, especially during intense rides or races. Here is a proprietary MotoSport guide to changing your Cobra BM50's coolant—made just for your bike.
Tools and Supplies Needed
- Fresh, pre-mixed motorcycle coolant suitable for aluminum radiators
- Socket/wrench set
- Pliers (if necessary for hose clamps)
- Clean rags
- Catch pan for old coolant
- Funnel
- Distilled water (for flushing, if desired)
- New sealing washer for the drain bolt (recommended)
- Gloves and safety glasses
Step-by-Step Coolant Change Procedure
- Let the engine cool completely. Never open the radiator cap while the engine is hot to avoid burns.
- Remove the seat and any bodywork that covers the radiator cap or coolant reservoir for easier access.
- Place your catch pan beneath the radiator drain bolt or the lower radiator hose. Positioning matters on the compact Cobra BM50—check under the left side of the engine for the most accessible drain point.
- Open the radiator cap slowly (if your BM50 has a fill cap on the radiator or expansion tank). This releases any pressure in the system.
- Drain the old coolant:
- Loosen and remove the radiator drain bolt OR detach the lower hose from the radiator. Allow coolant to flow into the catch pan.
- If equipped, also drain the small expansion tank by removing its hose and tipping it over the pan.
- Flush the system (optional but recommended):
- Reinstall the drain bolt or hose temporarily. Fill the radiator with distilled water, run the engine briefly, then shut off and drain again using the same process. Repeat until the water runs clear.
- Inspect hoses and clamps for any cracks or leaks unique to the BM50's high-vibration use. Replace worn parts as needed, especially around the small radiator and tight bends common on this model.
- Reinstall the drain bolt/hose with a new sealing washer to prevent leaks. Tighten securely but avoid over-tightening, as the aluminum threads can strip easily.
- Add fresh pre-mixed coolant:
- Slowly pour new coolant into the radiator or reservoir until full. Avoid trapping air by pouring slowly and using a funnel.
- Top up the expansion tank, if equipped, to the upper mark.
- "Burp" the system:
- Run the engine for several minutes with the radiator cap off. Gently rock the bike and blip the throttle to release any air bubbles.
- Shut the engine off. Once cool, recheck coolant level; add more if necessary.
- Reinstall the radiator and expansion tank caps. Wipe away any spills for a clean finish.
- Reattach bodywork and seat. Dispose of used coolant in accordance with local regulations.
Cobra BM50 Notes & Tips
- The 1998 Cobra BM50 is a high-performance, air-cooled mini motocross bike. Maintaining coolant quality is crucial—these engines run hot due to their compact cylinder design and race tuning.
- The radiator and hoses are smaller than on full-size bikes, so small leaks or air pockets can quickly lead to big problems. Double-check all connections and hose routing when reassembling.
- Use only motorcycle-specific coolant safe for aluminum parts. Car coolants may damage the water pump or radiator components over time.
- After the first ride, check the coolant level once the bike cools down and top off if needed.
Regular coolant changes can greatly extend the life of your Cobra BM50 and keep it running strong on the track. If you need OEM or performance parts during the process, always trust MotoSport for quick delivery and the best selection for your ride.
Related Shopping Categories
Shop Radiators for a 1998 Cobra BM50 Dirt Bike.
Shop Coolant for a 1998 Cobra BM50 Dirt Bike.
Shop Temperature Sensors for a 1998 Cobra BM50 Dirt Bike.
Shop Tools for a 1998 Cobra BM50 Dirt Bike.
Shop Radiator Hoses for a 1998 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.