How to Change the Coolant in a 1998 KTM 250SX: A MotoSport Guide

Shop parts for a 1998 KTM 250SX Dirt Bike.

If you own a 1998 KTM 250SX, you already understand the value of regular maintenance to keep your two-stroke running strong. Over time, the coolant in your dirt bike loses effectiveness, potentially leading to overheating and engine damage. Below, you will find a proprietary step-by-step MotoSport guide specific to your model, making the coolant change process straightforward and reliable.

Tools & Supplies You'll Need

  • Socket set or wrench (for drain and radiator screws)
  • Catch pan for old coolant
  • Fresh motorcycle coolant (40% coolant – 60% distilled water mix is recommended for the 1998 KTM 250SX)
  • Funnel
  • Shop towels or rags
  • Gloves and safety glasses

Preparation

  • Ensure the engine is completely cool before working on the cooling system to prevent burns or injury.
  • Support the bike securely on a stand and make sure it is upright.

Step 1: Locate and Remove the Radiator Cap

Begin by gently removing the radiator cap on the left radiator. This step prevents a vacuum from forming and allows the coolant to drain completely when you open the system.

Step 2: Drain the Old Coolant

  • Locate the coolant drain screw (typically at the bottom of the water pump or near the lowest point of the radiator system).
  • Position your catch pan beneath the drain screw, then carefully loosen and remove the screw. Allow all old coolant to fully drain out of the system.
  • If your 250SX has coolant drain bolts on both radiators, remove each to ensure complete drainage. Some models require tilting the bike slightly to the right (about 30 degrees) to aid the process.
  • Inspect both the drain screw and its sealing washer for signs of wear or damage. Replace if necessary to prevent leaks.

Step 3: Flush the System (Optional but Recommended)

For best results, you can briefly fill the system with distilled water, reinstall the drain screw, and run the engine for just a few seconds. Then repeat the draining process, removing any remaining old coolant or debris.

Step 4: Reinstall the Drain Screw

Ensure the drain screw is clean, the washer is intact, and tighten it securely to prevent leaks. Do not overtighten; follow the manufacturer's recommended torque specification if available.

Step 5: Fill with New Coolant

  • Pour a 40% coolant to 60% distilled water mixture slowly into the left radiator.
  • Remove the bleed screw located on the right radiator and tilt your motorcycle about 30 degrees to the right. Continue filling until coolant escapes bubble-free from the bleed hole.
  • Once air bubbles stop and only coolant comes out, immediately reinstall the bleed screw to ensure no air re-enters the system.
  • Return the bike to the upright position and add coolant to the left radiator until the level sits about 10mm (0.4 in) above the radiator fins.

Step 6: Final Checks

  • Reinstall the radiator cap.
  • Start the engine and let it run for 1–2 minutes, then switch it off and recheck the coolant level. Add more if necessary.
  • Check for leaks around the drain and bleed screws after a brief ride session.

Model-Specific Notes: 1998 KTM 250SX

  • The 1998 KTM 250SX uses approximately 0.5 liters (0.13 US gallons) of coolant in the system, so avoid overfilling to prevent overflow.
  • Always use high-quality coolant and distilled watertap water can introduce minerals and cause corrosion.
  • Inspect the rubber O-rings and hose connections on your radiators during a coolant change. Replace if cracked or brittle to avoid future leaks.
  • This model features a two-stroke engine with a robust liquid-cooling system. Overheating can cause serious internal damage, so perform a coolant change every two years or after severe rides.

Pro Tips for Carefree Riding

  • Always dispose of old coolant responsibly—never pour it down the drain or onto the ground.
  • Use a funnel to avoid spills, and immediately clean any coolant that contacts painted surfaces to prevent damage.
  • If you frequently ride in extreme temperatures, consider a coolant rated for superior temperature range and freeze protection.

Regular coolant changes keep your 1998 KTM 250SX running at peak performance. Trust MotoSport for the best OEM and aftermarket cooling system upgrades, replacement parts, and supplies—all designed for your ride.

Related Shopping Categories

Shop Radiators for a 1998 KTM 250SX Dirt Bike.

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Shop Temperature Sensors for a 1998 KTM 250SX Dirt Bike.

Shop Tools for a 1998 KTM 250SX Dirt Bike.

Shop Radiator Hoses for a 1998 KTM 250SX 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.