How to Change the Coolant in a 2018 Cobra CX50SR

Shop parts for a 2018 Cobra CX50SR Dirt Bike.

Maintaining your 2018 Cobra CX50SR is essential for top performance, especially when it comes to the cooling system. Routine coolant changes prolong engine life and ensure your bike is ready for anything on the track or trail. The CX50SR's high-performance two-stroke engine relies on a closed-loop coolant system that needs regular service. Below, you'll find a proprietary MotoSport step-by-step guide to safely changing the coolant, plus important model-specific notes for your CX50SR.

What You'll Need

  • Fresh coolant recommended for high-performance two-stroke engines
  • Drain pan
  • Phillips screwdriver or socket set (for radiator cap and bodywork)
  • Soft rags
  • Distilled water (for flushing, if needed)
  • Funnel
  • Gloves and eye protection

Preparation

  • Ensure the engine is completely cool to avoid burns.
  • Place the CX50SR on a stable stand and remove enough bodywork to access the radiator cap and lower hose or drain bolt.
  • Check your work area is well-ventilated and free of anything that could be damaged by spilled coolant.

Draining Old Coolant

  • Locate the radiator cap on top of the radiator and carefully unscrew it. If the system is pressurized (hissing or resistance), allow the engine to cool more before proceeding.
  • Either remove the lower radiator hose at the clamp or locate the coolant drain bolt (if equipped) at the base of the water pump and place the drain pan beneath the area.
  • Allow all coolant to drain completely into the pan. Be patient–a thorough drain is key for a complete change.
  • If your CX50SR overflow tank is dirty, carefully remove it, rinse with distilled water, and reinstall.

Flushing the System (Optional but Recommended)

  • Reinstall the radiator hose or drain bolt temporarily.
  • Fill the radiator with distilled water, reinstall the cap, and start the bike briefly—30 seconds is enough—to circulate water and loosen any residue.
  • Shut off the engine, let it cool, then drain again. Repeat until water runs clear.

Refilling with New Coolant

  • Securely reinstall the lower hose or drain bolt. Confirm all hose clamps are snug but not over-tightened.
  • Slowly pour fresh coolant into the radiator until it just reaches the base of the filler neck (use a funnel for accuracy).
  • Fill the overflow tank (if equipped) to the specified mark.

Bleeding Air from the System

  • With the radiator cap still off, start the engine and let it idle. Gently rock the bike side to side to help air bubbles rise.
  • Watch the coolant level–add a bit more if it drops as air escapes.
  • Once the coolant level stabilizes, install the radiator cap and allow the bike to reach full operating temperature.
  • Let the CX50SR cool down. Recheck the coolant level in both the radiator and the overflow tank. Top off as needed.

Dispose of Used Coolant Responsibly

  • Used motorcycle coolant is toxic. Take it to a proper recycling or waste facility.

CX50SR-Specific Notes & Tips

  • During initial break-in, it is normal for the CX50SR to lose up to 4 oz (120 ml) of coolant through the overflow–always check levels after the first rides and top up as needed.
  • Inspect the radiator fins for bending or debris and gently straighten as necessary.
  • Check radiator hoses for cracks, softness, or hardening. Replace them if any deterioration is found as high-performance engines demand a perfect seal.
  • Always use coolants suitable for high-revving, race-oriented two-stroke engines and never substitute with automotive coolant unless specified by Cobra.

Riding Confidently

With a fresh coolant change, your 2018 Cobra CX50SR is ready to keep its cool no matter how demanding the ride. Regularly maintaining your cooling system is vital for reliability and peak power, especially during intense race sessions and hot weather. Trust MotoSport for parts, advice, and expertise tailored to your ride.

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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.