How to Change the Coolant in a 2020 Cobra CX50JR

Shop parts for a 2020 Cobra CX50JR Dirt Bike.

Changing the coolant in your 2020 Cobra CX50JR is an essential maintenance routine that keeps your mini motocross bike running cool and prevents engine damage during hard riding. This guide provides step-by-step instructions and key CX50JR-specific tips to ensure proper service and reliability exclusive to MotoSport.com.

Required Tools & Supplies

  • Fresh coolant (preferably pre-mixed or mixed with distilled water)
  • Drain pan
  • Flat head screwdriver
  • Hex wrenches: 3mm, 4mm, 5mm, 8mm, 13mm
  • Clean rags

Step-by-Step Guide

  1. Cool Down the Bike:
    Let the engine cool completely to prevent burns and ensure accurate coolant levels.
  2. Access the Radiator:
    Remove any plastic covers obstructing the radiator cap.
  3. Drain Old Coolant:
    Remove the radiator cap. Place the drain pan under the water pump and open the drain bolt with the appropriate hex wrench.
    Inspect the drained coolant for evidence of oil, combustion byproducts, or debris. If you see a black "oil slick," consult a technician, as this may indicate engine trouble.
    For broken or damaged impellers, back flush the system to eliminate plastic pieces.––Check system according to OEM standards if you suspect issues.
  4. Flush the System (Recommended):
    Pour distilled water into the radiator, run the engine briefly, then drain the water to remove residual contaminants.
  5. Replace the Drain Bolt:
    Install a fresh sealing washer on the drain bolt and tighten securely.
  6. Fill with New Coolant:
    Pour fresh coolant slowly into the radiator neck, filling it to the base of the filler. Use only distilled water if mixing, never tap water, to protect the fine radiator passages from mineral deposits.
  7. Burp the Cooling System:
    Start the bike with the cap removed. Blip the throttle and gently rock the bike to free trapped air. Once the level drops, add more coolant to reach the base of the filler neck.
  8. Check Coolant Reservoir:
    Fill the reservoir to the upper line if equipped. This acts as an expansion tank for overflow and contraction cycles.
  9. Test the System:
    Reinstall the radiator cap. Run the engine until it reaches normal operating temperature. Let it cool to ambient, then re-check both the radiator and reservoir levels.

Specific CX50JR Owner Notes

  • Throttle Cable Strain Relief: Consider installing two 8-inch zip ties as a strain relief on the throttle cable where it enters the carburetor. This reduces the risk of the cable pulling out during aggressive riding and protects the cable top & adjuster. Cobra recommends zip tying the boot to the cable and securing the adjuster for best results.–This practical update is standard on new Cobra builds.–
  • CFD Gear Wear: If you notice the engine cover slipping or odd gear wear, the brass bushing may be letting the gear operate off-center. Ask about a CFD refresh kit if these symptoms appear.
  • Break-in Period: After coolant service or fresh engine builds, ride gently for the first half-hour, then recheck coolant level. Cobra recommends VP Racing X2 1050 premix oil with high-octane pump gas for best performance in your CX50JR.

Follow these exclusive instructions for your 2020 Cobra CX50JR to keep it running cool on every ride.—If you notice repeated coolant loss or symptoms like oil in the coolant, seek professional service and reference your owner’s manual for advanced water pump servicing.

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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.