How to Change the Coolant in a 2000 Cobra CM50

Shop parts for a 2000 Cobra CM50 Dirt Bike.

Maintaining the correct coolant level and condition is critical for the performance and longevity of your 2000 Cobra CM50 dirt bike. This two-stroke mini motocrosser is built for racing, requiring optimal cooling to handle the demands of competition. Changing the coolant is a straightforward, essential procedure that prevents overheating and internal damage, while keeping your Cobra's performance at its best. Follow this step-by-step MotoSport guide specific to the CM50 including important owner tips unique to this machine:

Preparation and Safety

  • Ensure the engine is completely cold before starting never remove the radiator cap when the engine is hot. The CM50's high-performance cooling system can retain pressure and cause scalding if opened while hot.
  • Support the bike upright on a stand and have safety gloves and eye protection on hand.
  • Gather supplies: suitable engine coolant (silicate-free, pre-mixed or mixed per container instructions), a drain pan, a 13 mm wrench, clean rags, and a funnel.

Step 1: Access the Cooling System

  • Locate the radiator cap at the top of the right radiator (side of the CM50).
  • Place your drain pan underneath the water pump on the lower right side of the engine.

Step 2: Drain Old Coolant

  • Carefully remove the radiator cap.
  • Remove the lower radiator hose where it connects to the water pump to allow all coolant to flow into your pan.
  • If needed, you may tilt the bike gently to ensure complete drainage.

Step 3: Inspect and Reassemble

  • Check hoses and clamps for cracking or looseness. The CM50 is designed for youth competition, so even small leaks can impact performance.
  • Reconnect the lower radiator hose firmly. Make sure it is tight and free of any trapped debris.

Step 4: Refill with Fresh Coolant

  • For the Cobra CM50, the typical coolant volume is 450–500 mL. Slowly fill the radiator until coolant is visible just above the radiator cores (the tubes and fins you see under the cap).
  • To avoid trapped air (airlocks can harm engine cooling), gently squeeze the top and bottom radiator hoses or lightly shake the bike to encourage bubbles to rise and escape. You may see bubbles "burp" out as air escapes.
  • Top off coolant as needed so the level remains just above the radiator cores.

Step 5: Bleed the System and Final Check

  • With the radiator cap off, start the engine and let it idle for 20-30 seconds. Shut off immediately if coolant level drops and refill if necessary.
  • Once the level remains stable and bubbles stop forming, install the radiator cap firmly and ensure it is sealed correctly – improper installation can lead to engine overheating or damage.
  • Let the engine run until warm, then shut off and allow to cool completely. Re-check coolant level; add more if it has dropped.

Special Notes for 2000 Cobra CM50 Owners

  • Some coolant loss (up to 4 oz / 120 mL) through the overflow hose during break-in is normal for this model. After break-in, monitor more closely for any abnormal fluid loss, which could indicate a leak.
  • Always use a radiator cap in good condition the CM50's pressurized system depends on the cap sealing fully.
  • For racing or heavy-duty use, check the coolant before every ride. Small bikes like the CM50 are less forgiving of low coolant than full-size machines.
  • Do not use plain water or automotive antifreeze with silicates – use coolant formulated for motorcycles.

Final Tips

  • If the drained coolant is clean and uncontaminated, it may be reused, but always replace it if in doubt or if it looks dirty or oily.
  • Document the coolant change date, and replace coolant at least once a year, or more often for competitive riders.

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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.