How to Change the Coolant in a 1985 Suzuki RM125
Shop parts for a 1985 Suzuki RM125 Dirt Bike.
Keeping your 1985 Suzuki RM125 running at peak performance means regular maintenance, and one of the most essential tasks is replacing the coolant. This ensures your engine stays cool, avoids overheating, and protects internal components. The RM125, known for its light weight and race-ready spirit, relies on a robust liquid cooling system—treat it well and it will return the favor on the track or trail.
What You'll Need
- Fresh coolant suitable for motorcycles (avoid car-specific types)
- Drain pan
- 10mm wrench or socket (for drain bolt)
- Rags for cleanup
- New crush washer (recommended for drain bolt)
- Funnel
- Protective gloves
Step-by-Step Coolant Change
- Cool the Bike: Make sure the engine is completely cool before starting. Hot coolant is dangerous.
- Remove the Radiator Cap: Loosen the radiator cap to release any built-up pressure in the cooling system; do this carefully.
- Locate the Drain Bolt: The RM125 coolant drain bolt is found at the water pump cover, on the lower right side of the engine. Position your drain pan underneath.
- Drain the Old Coolant: Loosen and remove the drain bolt. Allow the coolant to drain fully. Remove the lower radiator hose if necessary for a complete drain. Dispose of old coolant responsibly—never pour it down the drain.
- Check Components: Inspect the drain bolt washer (replace with a new crush washer for better sealing). Examine hoses and clamps for wear and cracks, and check the radiator fins for debris or damage—common issues that can affect cooling efficiency.
- Reinstall the Drain Bolt: Tighten the drain bolt securely but do not overtighten. Clean away any spilled coolant.
- Refill with New Coolant: Slowly pour fresh coolant into the radiator until full. Some fluid may make its way to the expansion tank.
- Bleed the System: With the radiator cap off, gently squeeze the radiator hoses to work out trapped air. Allow the bike to rest for a few minutes, topping off the coolant as it settles.
- Run the Engine: Start the engine and let it idle for about 5-10 minutes. Watch for air bubbles escaping the radiator filler neck—this indicates air is being purged, which is especially important for the RM125's high-revving, race-focused engine. Immediately shut off if you see leaks or problems. Let the bike cool, then check and top off coolant as needed.
- Install the Radiator Cap: Once you're sure the system is properly bled and filled, securely reinstall the radiator cap.
- Final Inspection: Double check for leaks around the drains, hoses, and radiator cap area. Go for a short ride, then re-inspect and confirm coolant levels once more after the bike cools down.
Special Tips for the 1985 Suzuki RM125
- The RM125 is known for its lightweight air-cooled predecessor, but the 1985 model uses a liquid cooling system that relies on fresh, high-quality coolant for peak performance and to avoid overheating or piston seizure.
- Over time, rubber hoses can harden or crack—inspect and replace them if needed. Poor hose condition is a common cause of leaks in older RM125s.
- Always use a new crush washer when reinstalling the drain bolt. It's an inexpensive way to prevent leaks and potential engine damage.
- If you notice frequent coolant loss, check the water pump seals and radiator cap for wear, as these are common failure points on this era of Suzuki dirt bikes.
- If you use your RM125 for racing or aggressive riding, consider performing a coolant change before and after each race season.
Why Proper Coolant Maintenance Matters
Keeping the cooling system in top shape helps prevent overheating and engine failure, which can be catastrophic—especially on the high-strung 1985 RM125. Timely coolant changes also protect the internal water pump, aluminum engine components, and ensure maximum performance on every ride.
Related Shopping Categories
Shop Radiators for a 1985 Suzuki RM125 Dirt Bike.
Shop Coolant for a 1985 Suzuki RM125 Dirt Bike.
Shop Temperature Sensors for a 1985 Suzuki RM125 Dirt Bike.
Shop Tools for a 1985 Suzuki RM125 Dirt Bike.
Shop Radiator Hoses for a 1985 Suzuki RM125 Dirt Bike.
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.