How to Change the Coolant in a 1991 Yamaha RT180: MotoSport DIY Guide
Shop parts for a 1991 Yamaha RT180 Dirt Bike.
The Yamaha RT180 is a classic two-stroke dirt bike known for its beginner-friendly design, reliable engine, and air-cooled simplicity. However, it includes a small coolant system for certain regions and years due to emission and temperature variations. Keeping the cooling system in peak condition is essential for performance and longevity. Follow this exclusive MotoSport.com step-by-step guide for changing the coolant in your '91 Yamaha RT180.
Supplies Needed
- Fresh pre-mixed motorcycle coolant (or concentrate plus distilled water for a 50/50 mix)
- Basic hand tools
- Drain pan
- Funnel
- Shop rags
- Gloves
Step 1: Prepare the Bike
- Start with a cool engine to avoid burns.
- Prop the bike upright, ideally on a stand, and remove the seat and side panels for access.
- Locate the radiator and the coolant reservoiron the RT180, these are easily accessible on the left side.
Step 2: Drain the Old Coolant
- Place a drain pan under the water pump area.
- Find the coolant drain bolt at the lowest point of the water pump cover (often a small bolt).
- Remove the radiator cap to allow air in and drain the system more quickly.–Do this slowly to relieve any pressure.
- Loosen the drain bolt and allow fluid to completely drain.
- Inspect the drained coolant for rust, oil, or debristhese may indicate further issues.
Step 3: Optional–Flush the System
- If the coolant appears dirty or neglected, flush with distilled water.
- Replace the drain bolt, fill the system with distilled water, reinstall the radiator cap, run the engine for a minute, then repeat the draining process.
- Repeat until only clean water drains out.
Step 4: Add New Coolant
- Ensure the drain bolt is secure (use a new sealing washer if necessary).
- Pour your fresh coolant slowly into the radiator with a funnel, filling to just below the filler neck.
- Squeeze the radiator hoses gently to help remove air pockets as you fill.
Step 5: Bleed the System
- With the radiator cap still off, start the engine and let it idle for several minutes.
- Gently blip the throttle and rock the bike side to sidethis helps burp out any trapped air bubbles.
- Add more coolant if the level drops.
- Once bubbles stop appearing and the coolant stabilizes, reinstall the radiator cap.
Step 6: Final Checks
- Run the bike up to operating temperature, then shut it off and let it cool fully.
- Double-check fluid levels and top off if needed.
- Properly dispose of all old coolant at a local hazardous waste facility.
- Reinstall bodywork and take your RT180 for a quick test ride, watching for leaks or overheating.
RT180-Specific Notes
- The '91 RT180 features a simple cylinder cooling system–no complex thermostats or electric fans to worry about. Maintenance is straightforward, but it's critical not to mix coolant types.
- Always use distilled water with concentrate coolants to prevent mineral deposits inside your Yamaha's narrow cooling channels.
- Inspect the radiator fins for clogs or damage–the air-cooled head relies on maximum airflow, especially in warm climates or slower trail rides.
By following these steps, you ensure your 1991 Yamaha RT180 runs cool and reliable, whether you're restoring a classic or just keeping your trail machine in top form.
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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.