How to Change the Coolant in a 1981 Kawasaki KDX80
Shop parts for a 1981 Kawasaki KDX80 Dirt Bike.
Maintaining your 1981 Kawasaki KDX80 means keeping the cooling system in peak condition–essential for performance and longevity. The KDX80 uses a simple, reliable liquid cooling system, but decades-old bikes like this often need extra attention to detail during maintenance. Read below for a proprietary MotoSport coolant change guide tailored to your classic 80cc two-stroke.
What You’ll Need
- Socket set (8mm and 10mm)
- Screwdriver
- Drain pan
- Funnel
- Distilled water
- Fresh motorcycle coolant (check your model for pre-mix or concentrate and mix with distilled water if needed, typically 50/50)
- Gloves and rags
Coolant Change Guide for the 1981 KDX80
- Always work on a completely cool engine to avoid burns and prevent pressure-related accidents.
- Remove the seat and side panels using your 8mm or 10mm socket to access the radiator cap and coolant overflow reservoir if equipped.
- Place the drain pan under the bike beneath the water pump area. Locate and remove the coolant drain bolt (usually at the lowest point of the water pump hulking out from the right side of the engine case). Loosen, then remove the radiator cap to allow fast, complete drainage.
- Flush the System:
- Temporarily re-fit the drain bolt.
- Slowly fill the system with distilled water, then remove the bolt to flush residual coolant and contaminants.
- Repeat this process once or twice for a thorough flush–vintage bikes can collect scale, so don’t skip.
- Inspect the Coolant Hoses & Radiator–A 1981 KDX80’s hoses and tank may have aged. Check for cracks, bulges, or corrosion and replace if needed. Classic radiators can accumulate internal buildup, so flushing is even more crucial.
- Reinstall the drain bolt securely. If possible, use a new crush washer to prevent leaks.
- Refill the cooling system with new coolant up to the base of the radiator filler neck. On KDX80s, there is usually no separate expansion tank; if yours has an aftermarket or custom-fit reservoir, also fill to the recommended level.
- "Burp" the system:
- Start the engine with the radiator cap off and allow the bike to idle for a few minutes, gently blipping the throttle to remove air pockets.
- Add coolant as needed to maintain the correct level.
- Once coolant consistently flows and no more bubbles rise, install the radiator cap securely.
- Test and Recheck:
- Let the engine cycle up to operating temperature, then completely cool down again.
- Check the coolant level – if necessary, top up.
- Inspect for leaks after a short test ride before replacing bodywork.
Model-Specific Tips for the 1981 KDX80
- Many early KDX80s saw hard use in youth racing. Inspect all cooling hardware for previous repairs, aftermarket parts, or stripped fasteners.
- Hose clamps and rubber parts are prone to aging. It’s smart to replace them with every coolant change or restoration.
- The stock radiator is susceptible to internal scale buildup. If flushing does not clear rusty or cloudy coolant, consider a radiator removal and professional service.
- Use only silicate-free motorcycle coolant for aluminum engine cooling systems. Avoid automotive coolants with additives that could damage the classic alloy engine internals.
- Always dispose of old coolant responsibly–it’s toxic to people and pets.
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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.