How to Change the Coolant in a 2017 Cobra CX50JR

Shop parts for a 2017 Cobra CX50JR Dirt Bike.

Maintaining the cooling system of your 2017 Cobra CX50JR is essential to ensure peak performance and engine longevity. This mini motocrosser is engineered with close tolerances and designed for competition, making regular coolant changes especially important. Below, MotoSport presents a proprietary, step-by-step guide for changing the coolant and maintaining the cooling system on your CX50JR–including tips specific to this model.

Tools & Supplies You'll Need

  • Flat head screwdriver
  • 3mm, 4mm, 5mm, 8mm hex keys
  • 13mm hex wrench
  • Water pump installation tool
  • Drain pan
  • New pre-mixed coolant (do not use tap water–only distilled)
  • Clean rags
  • Protective gloves

Step-by-Step Instructions for Coolant Change

  1. Preparation
    Ensure the bike is on a level surface and completely cool before beginning. Remove the seat and any body panels that obstruct access to the radiator cap and coolant reservoir.
  2. Drain the Old Coolant
    Place a drain pan underneath the radiator. Remove the radiator cap carefully. If equipped, undo the drain bolt or gently detach the lower radiator hose to let all coolant flow into the pan.
    Inspect the old coolant for signs of oil or black "oil slick" contamination–these may indicate engine issues that require professional attention.
    Drain the overflow reservoir as well, either by disconnecting it or using a syringe.
  3. Flush the System (if needed)
    If your CX50JR's impeller is damaged or there's debris in the system, back flush the cooling circuit to prevent blockages and overheating. You can also rinse the overflow tank with water and scrub it if it appears dirty.
  4. Inspect Hoses & Radiator
    Before refilling, squeeze radiator hoses to check for brittleness or cracks. Inspect hose clamps for tightness and check the radiator fins for damage. Straighten any bent fins using a small screwdriver.
  5. Refill with Fresh Coolant
    Reinstall the drain bolt (replace sealing washer if necessary). Fill the radiator slowly with pre-mixed coolant (recommended 50/50 mix if not pre-mixed) up to the base of the filler neck. Fill the reservoir tank to its upper mark.
  6. Burp the System
    Start the bike with the radiator cap off–let it idle for several minutes. Gently rock the bike. As air bubbles escape ("burping" the system), top off the coolant again to the proper level.
    Reinstall radiator cap securely after bleeding air.
  7. Check Coolant Levels
    Allow the engine to heat up sufficiently, then shut off and let cool fully. Recheck fluid levels in both radiator and reservoir, topping off if needed. Any loss in the reservoir after heat cycling is normal as air escapes; repeat the fill/check process until the level stabilizes.
  8. Final Steps
    Reinstall all removed components. Dispose of the old coolant properly according to local regulations.

Cobra CX50JR Model-Specific Notes

  • The cooling system on the CX50JR is compact but highly efficient; close tolerances mean any debris or air in the system can quickly cause overheating. Regular coolant changes are not just maintenance–they are critical for race performance and engine longevity.
  • During break-in and after each race, inspect coolant for any unusual contaminants as these can be early warning signs of potential internal issues.
  • Impeller access requires some disassembly of ignition and water pump components (covered above)–if you notice persistent overheating after a flush, inspect impeller condition.

Pro Tips from MotoSport

  • Always use high-quality, pre-mixed coolant formulated for motorcycles. Avoid automotive coolant blends unless specifically rated for MX two-stroke use.
  • Never mix tap water with coolant–use only distilled to avoid deposits.
  • Check all hose connections and clamps for tightness during every service.

Taking good care of your 2017 Cobra CX50JR's cooling system ensures consistent power delivery and protects your investment. For everything you need, MotoSport has you covered–Shop parts for a 2017 Cobra CX50JR Dirt Bike.

Related Shopping Categories

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Shop Radiator Hoses for a 2017 Cobra CX50JR 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.