How to Change the Coolant in a 1991 Yamaha YZ250: MotoSport Exclusive Guide
Shop parts for a 1991 Yamaha YZ250 Dirt Bike.
Proper maintenance of your 1991 Yamaha YZ250 is key to top performance on the track and trail, and refreshing your coolant can prevent costly overheating issues and keep your engine at its best. This MotoSport-exclusive guide walks you through the coolant change process and highlights specifics unique to this iconic two-stroke model.
What Makes the 1991 Yamaha YZ250 Cooling System Unique?
The 1991 YZ250 uses a liquid-cooled two-stroke engine designed for high-revving motocross performance. Its aluminum engine parts make it crucial to use high-quality ethylene glycol coolant with anti-corrosion additives for aluminum engines. Neglecting this can result in premature corrosion or scaling inside the cooling system.
Before You Begin
- Park the bike on a stable, level surface—let the engine cool completely before starting.
- Prepare safety gloves, rags, and a catch pan large enough for at least 1.27 US quarts of coolant (the YZ250 coolant capacity).
- Have a funnel, new coolant, and soft tap water ready for flushing.
Step-by-Step Coolant Change Process
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Remove the Radiator Cap
Slowly loosen and remove the radiator cap to release any residual pressure (ensure the engine is cool to avoid burns). -
Drain the Old Coolant
Place your catch pan under the engine area. Locate the coolant drain bolt (typically on the water pump cover) and carefully remove it, including the copper washer, to let the coolant fully drain.
Note: Ideally, remove also the lower radiator hose to ensure a more complete drain. -
Flush the System
Reinstall the drain bolt and washer temporarily. Fill the radiator with soft tap water. Reinstall the radiator cap, start the engine briefly (30 seconds), then shut down and drain again. Repeat until all previous coolant color and residue is gone. Flushing is key if switching coolant types or after overheating incidents. -
Install the Drain Bolt
Ensure the copper washer is in place. Tighten the drain bolt to 10 Nm (7.2 ft-lb) to prevent leaks – avoid overtightening. -
Refill with New Coolant
Mix coolant to a 50/50 ratio (coolant and soft water) if not pre-mixed. Slowly pour coolant to the base of the radiator neck. Pause during filling to let air pockets rise out – lightly tap hoses or gently squeeze them by hand to help bubble movement. -
Bleed and Recheck Levels
With the radiator cap open, start the bike and run it at low idle for a minute. Watch for air bubbles escaping. Shut down, let cool, and recheck coolant levels. Top off if needed. Install the radiator cap securely. -
Inspect for Leaks
Run the engine and check all fittings, the water pump cover, and radiator for drips or seepage. Address leaks immediately to avoid engine damage.
Important YZ250 Owner Tips
- Always replace the copper washer on the drain bolt to ensure a reliable seal each service.
- Use only aluminum-compatible coolant—standard automotive coolants can harm internal passages.
- If you notice milky coolant, inspect for water pump seal issues (a common two-stroke maintenance item).
- YZ250 radiators are vulnerable to crash damage; inspect for bent fins or leaks after any tip-over.
Recommended Interval
Change your YZ250's coolant at least once per year, or more often if you ride in harsh conditions or participate in frequent races.
Final Check
After the first ride, always recheck coolant level when the bike is cool to ensure the system is fully bled and topped off.
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.