How to Change the Coolant in a 1986 Suzuki RM125

Shop parts for a 1986 Suzuki RM125 Dirt Bike.

Keeping your 1986 Suzuki RM125 running cool is essential for top performance – especially on the trails and the track. Whether you’re tackling steep climbs, sweeping corners, or just enjoying the wilderness, a proper coolant change will extend the life of your engine and prevent expensive repairs. Here’s a MotoSport-exclusive guide to replacing your coolant correctly, plus what makes your RM125's cooling system unique.

Preparation – What You’ll Need

  • Fresh coolant (consult the owner’s manual for recommended type)
  • Drain pan
  • Ratchet – 10mm socket
  • Phillips screwdriver or Allen wrench (for radiator shrouds)
  • Distilled water for flushing
  • Safety gloves & eye protection

Important: Only work on your cooling system when the engine is stone-cold. Hot systems are pressurized – opening components risks burns and property damage.

Step 1: Remove the Radiator Cover

  • Use your Allen wrench or screwdriver to remove the four bolts securing the radiator shroud. Set the shroud aside and inspect for dirt or debris. Clean as needed to ensure proper airflow through the radiator fins.

Step 2: Drain the Old Coolant

  • Locate the coolant drain bolt – typically at the bottom of the water pump housing on the right engine case.
  • Place your drain pan beneath the drain area. Use a 10mm socket to remove the bolt and allow coolant to flow out completely.
  • Remove the radiator cap to speed the draining process and inspect the cap for corrosion or contamination. Replace if necessary.

Step 3: Flush the Cooling System

  • After the system drains, pour distilled water into the radiator and let it flow through with the drain bolt out. This helps remove any residual old coolant and mineral buildup.
  • Repeat the flush until water runs clear.

Step 4: Replace Drain Bolt – Add Fresh Coolant

  • Reinstall the drain bolt securely.
  • Fill the radiator with new coolant until it covers the internal fins but doesn’t overflow.
  • Reinstall the radiator cap.

Step 5: Bleed the System – Recheck Levels

  • Start the RM125 and let it idle for several minutes. Watch for air bubbles escaping from the overflow hose (if equipped).
  • Shut off the bike, let it cool fully, and re-check coolant level. Top-off as needed – do not overfill.

Model-Specific Notes for the 1986 RM125

  • The RM125 uses a compact single-radiator system. Monitor the radiator for physical damage after each ride – bent fins or cracks can cause overheating.
  • The 1986 model’s water pump and hoses are easily accessible, but check for leaks after any coolant service.
  • This year’s bike may be fitted with older hose clamps – inspect them and upgrade if they show signs of wear to prevent leaks.
  • Always use the recommended coolant type. Silicate-containing formulas can damage water pump seals over time.

Proper coolant changes every season keep your RM125 ready for its next big adventure – and help you avoid costly engine damage. Got questions about your RM’s cooling system or ready for an upgrade? Shop genuine and aftermarket parts for your 1986 Suzuki RM125 right here at MotoSport.

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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.