How to Change the Coolant in a 1992 Suzuki RM125

Shop parts for a 1992 Suzuki RM125 Dirt Bike.

Keeping your 1992 Suzuki RM125 running cool on the trail means regular maintenance of the cooling system. Changing the coolant is a straightforward process, but there are specific steps and model quirks to keep in mind.

Supplies Needed

  • Fresh coolant premixed 50:50 with distilled water
  • Catch pan or bucket
  • 10 mm socket or wrench
  • Clean rags
  • Funnel
  • Gloves (recommended)

Step-by-Step Coolant Change Guide

  1. Let the engine cool completely.
    Never open the radiator cap when the engine is hot – scalding steam or fluid can cause serious injury.
    Wait until the engine has cooled down.
  2. Remove the shroud if needed.
    For easier access, take off the left side radiator shroud by removing the three screws using an 8 mm socket.
  3. Open the radiator cap.
    Gently twist and remove the radiator cap; this releases any trapped pressure for safer draining.
  4. Locate the coolant drain bolt.
    Find the drain bolt at the bottom of the water pump casing (most often 10 mm) near the engine's left side.
    Place your catch pan underneath to collect the old coolant.
  5. Remove the drain bolt and fully drain the coolant.
    Unscrew the bolt carefully and allow all coolant to drain out.
    Inspect the coolant – if it appears rusty, milky, or sludgy, flushing the system with distilled water is a good idea before refilling.
  6. Reinstall the drain bolt.
    If your drain bolt uses a sealing washer, check its condition and replace if necessary. Tighten the bolt gently to avoid stripping the threads.
  7. Refill with fresh coolant.
    Slowly pour coolant (50:50 mix of antifreeze and distilled water) into the radiator until it reaches the bottom of the inlet hole at the radiator cap opening.
    Do not overfill. The RM125 does not have an overflow tank—small drops in level are normal over time, so check before each ride.
  8. Secure the cap and shroud.
    Ensure the radiator cap is locked firmly—improper sealing causes pressure loss and coolant overflow.
    Replace the radiator shroud if you removed it.
  9. Start the engine and check for leaks.
    Run the bike for a few minutes to circulate the coolant. Stop, let the bike cool, and recheck the coolant level. Top off if needed.

What Makes the 1992 RM125 Cooling System Noteworthy?

  • No overflow tank: Unlike many newer bikes, your RM125 lacks a coolant reservoir. The system is direct-fill, so frequent coolant checks are important.
  • Routine checks: Check the coolant level at the radiator before every ride for best engine protection.
  • Cooling performance: Fresh coolant helps prevent overheating and corrosion—essential for the high-strung RM125 two-stroke powerplant.

Pro Tips for RM125 Owners

  • Inspect hoses and clamps while changing the coolant for signs of fatigue, cracking, or leaks—these inexpensive parts are crucial for reliability.
  • Use only coolant rated for aluminum engines, mixed with distilled water, to prevent corrosion and maximize cooling efficiency.
  • Upon refilling, tilt the bike upright and gently rock it to help burp any trapped air bubbles from the system.
  • If you ride hard or race, consider flushing the system annually, not just every two years.

Changing the coolant in your 1992 Suzuki RM125 is essential maintenance that safeguards engine performance & longevity. Take a few minutes every season to keep your ride running cool—and rely on MotoSport for all your genuine RM125 parts and service needs.

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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.