How to Change the Coolant in a 2018 Cobra CX50JR

Shop parts for a 2018 Cobra CX50JR Dirt Bike.

The 2018 Cobra CX50JR is a high-performance mini motocross bike with a unique cooling system, emphasizing regular coolant maintenance for peak performance. Owners should note that losing up to 4 oz (120 ml) of coolant over time is normal–the proper coolant level covers the tops of the radiator cores, visible only by removing the radiator cap and inspecting inside5.

Step-by-Step Coolant Change Guide

  • Preparation
    Ensure the bike is on a stable work surface and has cooled to ambient temperature to avoid burns. Gather necessary tools–typically a flathead screwdriver and hex keys (commonly 3mm, 4mm, and 13mm for CX50JR hardware)4.
  • Drain the Old Coolant
    Remove the radiator cap. Use the drain plug located at a low point on the water pump cover to empty coolant into a safe container for proper disposal3. Inspect removed coolant for oil slicks or combustion byproducts, which may indicate internal problems4.
  • Flush the System (Optional but recommended for older bikes)
    Flush with distilled water–avoid tap water, as minerals can damage the radiator2. For heavily neglected systems, flush briefly with a 50/50 mix of distilled water and vinegar, run the engine to circulate, then flush again with distilled water and drain completely3.
  • Refill with New Coolant
    Pour the recommended premixed motorcycle coolant into the radiator up to the filler neck, slowly to minimize air pockets2. Do not overfill–ensure coverage of radiator cores. Squeeze coolant hoses and gently rock the bike to release trapped air bubbles3.
  • Burp the System
    With the radiator cap off, run the engine for a few minutes, gently revving and rocking the bike. This helps expel air and ensures complete circulation1. Recheck coolant level, top off as needed, then reinstall the radiator cap.
  • Check Expansion & Reservoir
    After heat-cycling to operating temperature, let the engine cool. Check the reservoir level again–it acts as an expansion tank, so minor changes are normal1. If repeated large losses occur, investigate for leaks or system problems.
  • Final Inspection
    Before riding, confirm the radiator is filled to the base of the filler neck and the reservoir tank is at the upper fill line3. After your next ride, double-check both levels.

Notes Specific to the Cobra CX50JR

  • This bike's compact radiator and water pump mean that minor coolant loss is typical. If you consistently lose more than 4 oz (120 ml), check for leaks or impeller damage.
  • Radiator cap removal is the only reliable way to check coolant level, as sight glasses are not present5.
  • If servicing the water pump or impeller, use the correct Cobra service tools and reference factory torque specs for reassembly4.
  • Always use a recommended motorcycle coolant–never plain water or automotive types, which can cause overheating or corrosion.

Following these steps will ensure your Cobra CX50JR stays running cool and strong on the track. Regular checks and scheduled coolant changes protect your investment and maximize 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.