How to Change the Coolant on a 1975 Suzuki RM125
Shop parts for a 1975 Suzuki RM125 Dirt Bike.
Keeping the cooling system of your 1975 Suzuki RM125 in top condition is essential for reliable performance – especially given this model's classic status and unique aluminum radiator design. Proper coolant maintenance prevents overheating, protects internal engine components, and preserves your bike's value.
What Makes the 1975 RM125 Unique?
- Aluminum radiator: Use only coolants compatible with aluminum parts to prevent corrosion.
- 2-stroke classic: The RM125 is oil-injected, so always ensure coolant can't mix with engine oil.
- Vintage components: Original hoses and fittings may be brittle – inspect closely and consider replacing any worn parts.
Before You Start
- Prepare a drain pan and basic hand tools (8mm socket or wrench for water pump bolt).
- Have aluminum-safe diluted coolant (typically 50:50 with distilled water) ready, as specified for the RM125.
- Work with a cool engine and make sure the bike is stable on a stand.
Step-by-Step Coolant Change Instructions
- Remove the skid plate or any covers obstructing access to the water pump or drain area.
- Drain the old coolant:
- Locate the water pump (bottom of the engine, clutch side) and remove the drain bolt.
- Remove the radiator cap to allow air in – this helps drain fully.
- Caught coolant should be disposed of at a recycling facility to protect the environment.
- Flush the Radiator:
- Pour distilled water through the radiator filler neck to remove old coolant and debris.
- Let it fully drain out the open drain before reinstalling the bolt (with a new crush washer, if available, for a tight seal).
- Refill with New Coolant:
- Mix new coolant to a 50:50 ratio if not pre-mixed – always with distilled water for the RM125's aluminum system.
- Fill through the radiator cap opening, up to the filler neck base.
- Bleed (Burp) the System:
- Start the engine with the radiator cap off, let it idle for several minutes, and gently rock the bike side to side.
- This allows air bubbles to escape; watch for circulation as coolant level may drop.
- Add more coolant as needed, until stable at the filler neck base.
- Replace the radiator cap.
- Check for Leaks and Final Level:
- Let the bike fully cool, then re-check the coolant level and top off if needed.
- Inspect all hose connections and the drain bolt for leaks.
Additional Tips for 1975 RM125 Owners
- Coolant type: Avoid silicate-based antifreezes that can damage the vintage aluminum radiator.
- Inspect often: Old seals, caps, and hoses may fail after decades – consider replacements before a major ride.
- Tighten cautiously: Aluminum threads and fittings can strip – do not overtighten the drain or radiator cap.
Routine coolant maintenance on your vintage Suzuki RM125 ensures long life for your classic two-stroke. If you need parts, check out the full range available above to keep every ride running cool.
Related Shopping Categories
Shop Radiators for a 1975 Suzuki RM125 Dirt Bike.
Shop Coolant for a 1975 Suzuki RM125 Dirt Bike.
Shop Temperature Sensors for a 1975 Suzuki RM125 Dirt Bike.
Shop Tools for a 1975 Suzuki RM125 Dirt Bike.
Shop Radiator Hoses for a 1975 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.