How to Change the Coolant in a 2002 Cobra CM50: MotoSport Guide

Shop parts for a 2002 Cobra CM50 Dirt Bike.

Regular coolant changes are essential for keeping your 2002 Cobra CM50's high-revving two-stroke engine running efficiently and protected from overheating. The Cobra CM50 uses a liquid-cooled system that is sensitive to dirt and improper coolant types, so following a proven process with the right products is critical. Below is a step-by-step guide unique to MotoSport and specific to your CM50 dirt bike.

Why Coolant Maintenance Is a Must for Your Cobra CM50

The Cobra CM50's small, competition-grade engine demands optimal cooling – clogged or contaminated coolant can increase cylinder temperatures, risking expensive damage. Cobra specifically recommends Liquid Performance Propylene Glycol based Mini Coolant / Antifreeze in the CM50 for the best results and safest engine operating temperatures. Always check your radiator and cooling system for debris or damage during maintenance, as dirty cooling fins reduce efficiency†.

Tools & Supplies Needed

  • Liquid Performance Propylene Glycol based Mini Coolant / Antifreeze (or Cobra-approved equivalent)
  • Drain pan
  • 13 mm socket or wrench
  • Ratchet or spanner (as needed)
  • Medium-strength (blue) thread locker
  • Ultra black Hi-Temp RTV silicone or Teflon pipe sealant
  • Clean rags
  • Protective gloves

Cobra CM50 Coolant Change Instructions

  1. Preparation
    Ensure the bike is cool to the touch. Park it on a stable, level surface and remove the seat, fuel tank, and exhaust pipe as needed for better access to the radiator and drain plug.
  2. Draining the Old Coolant
    • Remove the radiator cap to release any pressure.
    • Locate the 13 mm coolant drain plug (generally found near the bottom of the water pump on the right side of the engine).
    • Place a drain pan underneath and remove the plug, allowing coolant to fully drain out.
    Tip: Dispose of the used coolant responsibly, as it is toxic to animals and the environment.
  3. Inspect and Clean
    • Check the condition of radiator hoses and the radiator itself for clogs, leaks, or excessive dirt. Clean any external debris from the radiator fins.
    • Inspect the sealing washer of the drain plug and replace if damaged. Apply recommended sealant to pipe threads, as needed.
  4. Reassembly
    • Reinstall and torque the drain plug to spec (usually 11 ft-lb / 15 Nm for Cobra small-displacement engines). Use blue thread locker and ensure a proper seal.
    • If you performed impeller or shaft service, be sure to fit new bearings and seals as required, with the open side of the seal facing the impeller.
  5. Add New Coolant
    • Pour Liquid Performance Propylene Glycol based Mini Coolant / Antifreeze slowly into the radiator, filling to the base of the filler neck.
    • Reinstall the radiator cap only once the system is fully filled and air has been purged.
  6. "Burp" the System
    • Start the engine, with the radiator cap still off at first, and let it idle for a few minutes. Gently rock the bike to release air bubbles.
    • Add more coolant if the level drops, repeating until no more bubbles emerge.
    • Shut off the engine, install the cap, and check the reservoir level if equipped.
  7. Final Checks
    • Let the engine completely cool, then check the coolant level again. Top off as needed.
    • Inspect for leaks around hoses, the drain plug, and the radiator cap area.

What CM50 Owners Should Know

  • This model favors Propylene Glycol-based coolants; using conventional ethylene glycol or mixing coolant types is not recommended and can reduce performance and engine life.
  • If you need to service the water pump impeller or its shaft/seal, follow Cobra guidelines – an excessively worn shaft or leaky seal could allow coolant into the transmission/oil side, which must be avoided.
  • Overheating can cause serious engine damage. Regularly cleaning the radiator fins and ensuring proper coolant flow is essential, especially during track riding or in dusty conditions.

Keep your 2002 Cobra CM50 in championship condition with regular cooling system maintenance, using only the best parts and supplies for your ride.

<.-- † Based on Cobra CM50 owner's manual and factory recommendations. -->

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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.