How to Change the Coolant in a 1991 KTM 300EXC

Shop parts for a 1991 KTM 300EXC Dirt Bike.

Regular coolant changes are crucial to keep your 1991 KTM 300EXC running cool and preventing potential engine damage. This two-stroke legend is known for its robust power and lightweight chassis, but maintaining the cooling system is essential to avoid overheating on the trail. Follow this MotoSport.com guide for a smooth and effective coolant change tailored to your dirt bike.

What You Need

  • Fresh coolant (refer to your manual, typically 1.2 L or 1.3 qt. for the 300EXC)
  • Drain pan
  • Socket or wrench for drain screw
  • Clean rag
  • Distilled water (for flushing, if desired)
  • Rubber gloves (recommended)
  • Optional: compressed air (if switching coolant types or for thorough flushing)

Changing the Coolant: Step-by-Step

  • Let the engine cool completely. Never attempt to remove the radiator cap or drain coolant from a hot engine–the system is pressurized and can cause burns.
  • Position the motorcycle upright, securely supported. If possible, slightly jack up the front end–this helps air escape from the system during bleeding and refilling.
    (A poorly bled cooling system will reduce effectiveness and may cause engine overheating.)
  • Remove the radiator cap gently to relieve any residual pressure.
  • Place a drain pan underneath the water pump area.
  • Locate and remove the drain screw on the water pump cover. Allow all coolant to drain out completely.
    The 1991 KTM 300EXC uses a drain screw on the water pump, easily accessible from the side.
  • Optional: Flush with distilled water if you notice contamination or are switching coolant types. Replace the drain screw temporarily, fill the system with distilled water, start the engine for a minute (do not let it overheat), then drain again.
  • Reinstall the drain screw with a new seal ring (recommended for best sealing) and tighten securely, but avoid over-tightening.
  • Fill the radiator completely with fresh coolant. Pour slowly to prevent air pockets. The 300EXC holds about 1.2 L (1.3 qt.) of coolant.
    Fill until coolant escapes without bubbles from the bleeder screw, if available, or until the radiator is full to the neck.
  • Bleed the cooling system:
    • Loosen the bleeder screw on the cylinder head, if equipped, until coolant escapes without bubbles, then retighten.
    • Gently rock the bike side to side to encourage trapped air to escape.
    • Double-check that the radiator is still full after bleeding.
  • Install the radiator cap securely.
  • Run the engine briefly until it reaches operating temperature, then allow it to cool and re-check the coolant level. Top up as needed.

1991 KTM 300EXC Owner Notes

  • Check hoses and seals for signs of wear or aging. Replace as needed to prevent leaks that can lead to overheating.
  • Avoid mixing coolant types (e.g., don't mix silicate and non-silicate coolants). If switching, thoroughly flush the system first.
  • The dual radiator system connects both radiators in parallel. Ensure both are fully drained and filled, as air can become trapped if only one side is serviced.
  • Inspect radiator fins for mud or debris. Clean gently if clogged to enhance cooling efficiency.

Maintaining the cooling system on your 1991 KTM 300EXC ensures maximum performance and engine life, whether you’re tackling the trails or hitting the track. For quality replacement parts and fluids, remember to Shop parts for a 1991 KTM 300EXC Dirt Bike.

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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.