How to Change the Coolant in a 1987 Suzuki RM125: MotoSport Proprietary Guide

Shop parts for a 1987 Suzuki RM125 Dirt Bike.

Regularly changing the coolant in your 1987 Suzuki RM125 is critical for maximizing your bike's performance and longevity. This iconic two-stroke dirt bike requires attentive maintenance of its cooling system to prevent overheating, ensure smooth running, and guard against component damage.

Before You Begin: Essentials & Model-Specific Notes

  • Coolant Type: Always use a high-quality premixed coolant compatible with aluminum radiators. Avoid tap water–distilled water is recommended for flushing the system.
  • Tools Needed: Socket set (typically 8mm or 10mm for drain bolt), rag, pan for draining, distilled water for flushing, and replacement coolant.
  • Model-Specific Tip: The '87 RM125 features a relatively compact cooling system, which can be prone to air pockets during refill. Bleeding thoroughly is essential for avoiding engine overheating.
  • Environmental Care: Dispose of old coolant at an authorized recycling center. Never release it into the environment.

Step-by-Step: Changing the Coolant

  1. Preparation
    • Place the RM125 on a level surface and ensure the engine is cool.
    • Remove the seat and, if necessary, the side panels and skid plate for easy access.
  2. Drain Old Coolant
    • Locate the radiator cap (top of left radiator) and the coolant drain bolt (typically at the bottom of the water pump on the right side).
    • Loosen the radiator cap to release pressure.
    • Place your drain pan underneath and carefully remove the drain bolt. Allow all coolant to drain out completely.
  3. Flush the System (Highly Recommended)
    • Reinstall the drain bolt temporarily.
    • Pour distilled water into the radiator to flush out residue and contaminants.
    • Remove the drain bolt to let the water flush out; repeat until water runs clear. Avoid using tap water due to mineral deposits that can harm the cooling system.
  4. Refill with New Coolant
    • Replace and tighten the drain bolt securely.
    • Slowly add the correct coolant mix to the radiator until full, avoiding overfilling.
    • Let the bike sit briefly to allow bubbles to escape.
    • Some models may have a bleed screw on the radiator–if equipped, loosen slightly during refill to help release trapped air, then retighten.
  5. Bleed and Heat Cycle
    • Start the engine and let it idle, watching for air bubbles at the radiator neck. Gently rev the engine for a minute to help move coolant and release air.
    • Once the engine reaches operating temperature, shut it off and let it cool completely.
    • Recheck the radiator and overflow tank levels, and top off if needed–loss of coolant may indicate trapped air being released.
  6. Final Checks
    • Inspect for leaks around the water pump, radiator cap, and hoses.
    • Wipe down the bike, reinstall any panels, and confirm that all fasteners are secure.

Pro Tips for the 1987 RM125 Owner

  • The 1987 RM125 is a two-stroke–it does not have a thermostat, so thorough bleeding is even more critical for complete coolant circulation.
  • Watch your coolant level after the first ride. Minor reductions in the overflow tank are normal as trapped air escapes, but persistent drops may signal a leak or incomplete bleed.
  • Replace radiator hoses if they show signs of cracking, bulging, or excessive wear during coolant service.

Quick Maintenance Reminders

  • Change coolant every season or after extended periods of storage.
  • Never substitute engine oil for transmission fluid, as the RM125 uses a premix of gasoline and oil separately from the cooling system.

Looking after your 1987 Suzuki RM125 cooling system preserves its legendary two-stroke power and keeps every ride as exhilarating as the last. For anything you need—from fresh coolant to replacement hoses—MotoSport delivers the right solutions for vintage and race-ready performance.

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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.