How to Change the Coolant in a 1991 Kawasaki KX250
Shop parts for a 1991 Kawasaki KX250 Dirt Bike.
Routine coolant replacement is essential for keeping the 1991 Kawasaki KX250 running cool and at peak performance. The cooling system on this model consists of two radiators, hoses, and a water pump. Old coolant can corrode key components or lead to overheating, which is especially important to avoid on older two-strokes like the KX250. Here is a complete, proprietary MotoSport guide to changing your KX250s coolant safely and effectively.
What You Need
- 8mm wrench and 10mm socket
- Phillips screwdriver
- Clean rags
- Drain pan
- Fresh coolant (50% ethylene glycol-based antifreeze – 50% soft water)
- Gloves and safety glasses
Steps to Change Coolant
- Cool the Engine
Always allow the engine to cool completely before you start—removing the radiator cap when hot can result in serious burns. - Position the Bike
Set your KX250 on a level surface and a stand, upright and perpendicular to the ground for stability during service. - Remove the Radiator Cap
Twist the radiator cap counterclockwise to the first stop and pause. Fully depress and turn to remove, relieving any residual pressure in two steps to avoid coolant spray. - Locate and Remove the Drain Bolt
Find the drain bolt on the right side of the cylinder near the water pump cover (8mm bolt). Position a pan underneath and remove the bolt to drain old coolant from the engine and radiator. - Optional: Open Bleeder Screw
If equipped, loosen any radiator bleeder screw or auxiliary fill plug with a Phillips screwdriver to let air in and help fluid drain evenly. - Flush (Recommended for Best Results)
For a thorough job, flush the system with distilled water to remove mineral buildup. Reinstall the drain bolt and fill with water, run momentarily, then drain again. - Reinstall Drain Bolt
Tighten the drain bolt securely, replacing its washer if damaged to prevent leaks. - Add New Coolant
Mix 50–50 soft water and ethylene glycol antifreeze, formulated for aluminum radiators. The system requires approximately 0.96 liters (1 US quart). Slowly fill the radiator to the filler neck. - Bleed Air from the System
Briefly loosen the bleeder to release trapped air, then tighten. Top off if level drops. - Replace the Radiator Cap
Ensure the coolant is at the filler neck, then reinstall the cap securely. - Check for Leaks, Test Run, and Recheck
Start the bike and let it idle until warm. Shut off, allow to cool, then recheck coolant level. Top up if needed.
Notes for 1991 Kawasaki KX250 Owners
- This model uses an aluminum cylinder head and radiators; always use coolant designed for aluminum to avoid internal corrosion.
- The KX250 has a simple, gravity-fed cooling system—no thermostat—so bleeding air pockets after a refill is critical for proper function.
- Inspect all hoses, clamps, and the radiator cap for aging or wear; BMW-style radiators can become brittle and develop leaks after decades of use. MotoSport carries direct fit replacements.
- Always follow Kawasaki-specified ratios and capacities for coolant mix to avoid boiling or freezing problems.
Keeping the cooling system in prime condition will help your 1991 KX250 run strong on the track or trail for many more seasons.
Related Shopping Categories
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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.