How to change the coolant in a 1991 Yamaha XT350 Dirt Bike

How to Change the Coolant in a 1991 Yamaha XT350: Step-by-Step Guide

Shop parts for a 1991 Yamaha XT350 Dirt Bike.

Keeping your 1991 Yamaha XT350 running cool is essential for both performance and longevity. One of the most important yet overlooked maintenance tasks is performing a regular coolant change. This vintage dual-sport is known for its reliable air-cooled and liquid-cooled hybrid design, and old, deteriorated coolant can accelerate corrosion or cause overheating. Below is the proprietary MotoSport guide for changing coolant specific to the '91 XT350.

Tools and Supplies Needed

• Fresh, motorcycle-specific coolant (pre-mixed or mix with distilled water as instructed by the product)
• Socket wrench set
• Drain pan
• Funnel
• Distilled water (for flushing)
• Shop towels
• Gloves

Preparation

• Ensure the engine is completely cool to avoid burns and high-pressure release.
• Secure the XT350 on a stable stand or flat surface.
• Remove any side panels or tank covers as needed for easy access to the radiator and drain plug.

Drain the Old Coolant

• Locate the coolant drain bolt, usually situated at the lowest point of the XT350's water pump cover.
• Position the drain pan beneath the bolt and remove the radiator cap to allow air in.
• Unscrew the drain bolt and allow the coolant to completely empty into the pan.
• If your XT350 has a coolant reservoir tank, detach the overflow hose and drain it as well.

Flush the Cooling System (Recommended for Older Bikes)

• Reinstall the drain bolt finger-tight and fill the system with distilled waternot tap waterto flush any residual coolant or debris.
• Start the engine and let it idle for a few minutes (do not allow it to overheat). Turn off, cool, then drain again.
• Repeat until drained water runs clear.

Fill with Fresh Coolant

• Ensure the drain bolt is tightened securely with a fresh sealing washer if needed.
• Use a funnel to pour the new coolant into the radiator fill neck up to the lower rim.
• If the coolant comes as a concentrate, pre-mix it 50–50 with distilled water.
• Fill the reservoir, if equipped, up to the full line.

Remove Air (Burping the System)

• Start the engine with the radiator cap off and let it idle.
• Gently squeeze the radiator hoses and rock the bike to help trapped air escape.
• Top off coolant as it settles. Repeat until the level stabilizes at the filler neck.
• Install the radiator cap and run the engine to full operating temperature.
• Shut off, let the engine fully cool, and recheck the level. Top off all tanks as needed.

Key Tips for the 1991 Yamaha XT350 Owner

• The XT350's hybrid air/liquid cooling system makes proper coolant levels especially critical for avoiding top-end overheating on technical rides or slow trails.
• Inspect all hoses for cracks. The rubber can deteriorate faster on vintage bikes, so replace if there are any signs of failure.
• Avoid using tap water—minerals will accumulate inside the narrow cooling fins, reducing efficiency.
• Dispose of old coolant responsibly at a recycling center or auto parts shop—never dump it outdoors.

Conclusion

Changing the coolant on your 1991 Yamaha XT350 is both straightforward and vital. A routine flush and refill every two years will help your engine keep cool, prevent internal corrosion, and keep your classic dual-sport running mile after mile. For top-quality OEM and aftermarket cooling parts, fluids, and upgrades, MotoSport has you covered.

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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.