How to Change the Coolant in a 1978 Suzuki RM250

Shop parts for a 1978 Suzuki RM250 Dirt Bike.

Changing the coolant in your vintage 1978 Suzuki RM250 is one of the most important maintenance tasks to safeguard engine health, especially during demanding rides or in extreme environments. This classic two-stroke dirt bike lacks a coolant overflow reservoir, so routine checks and correct coolant procedures are critical to avoid overheating and engine damage.

Important Safety Precautions

  • Never open the radiator cap when the engine is hot - wait until it's completely cool to prevent injury from scalding steam or fluid.
  • Handle coolant carefully - avoid skin and eye contact, and keep it away from children and pets.
  • Dispose of used coolant responsibly, following local municipal guidelines.

Tools & Supplies Needed

  • Socket set or spanner
  • Drain pan
  • Fresh engine coolant (pre-mixed with distilled water, 50:50 ratio recommended)
  • Distilled water for flushing
  • Clean rag or towel
  • Protective gloves

Step-by-Step Coolant Change Procedure

  1. Ensure the Bike Is Cool
    Make sure your RM250 is on level ground, turned off, and the engine and radiator are completely cold.
  2. Remove the Radiator Cap
    Carefully loosen and remove the radiator cap to relieve any residual pressure.
  3. Drain the Old Coolant
    Locate and remove the coolant drain bolt at the base of the water pump.
    Let the old coolant flow completely into your drain pan.
  4. Flush the System (Recommended)
    Pour distilled water into the radiator and allow it to drain, repeating until the water runs clear. This helps prevent residue and scale in the cooling system.
  5. Reinstall the Drain Bolt
    Replace the drain bolt and tighten it securely. If your model uses a sealing washer, inspect and replace it if necessary to ensure a leak-free seal.
  6. Add New Coolant
    Slowly pour pre-mixed coolant into the radiator until the level reaches the bottom of the filler neck.
  7. Bleed Air from the System
    Gently rock the bike side-to-side to help trapped air escape. If equipped, loosen the air bleeder bolt on the cylinder head until coolant flows out, then retighten.
  8. Start the Engine Briefly
    With the radiator cap off, start the engine and let it run for 1-2 minutes. Watch for air bubbles escaping. Shut the engine off, then top up coolant if necessary.
  9. Secure the Radiator Cap
    Reinstall and fully tighten the radiator cap. Ensure it locks firmly to allow proper system pressure and avoid leaks.
  10. Check for Leaks & Cleanup
    Wipe away any spills, check for leaks, and properly dispose of your old coolant.

Key Notes for 1978 Suzuki RM250 Owners

  • No Coolant Overflow Tank – This model does not have a reservoir, so inspect coolant level at the radiator before every ride. Loss during operation is more likely.
  • Coolant Capacity: Approximately 850–950 ml. Overfilling can cause overflow, improperly tightening the radiator cap can cause leaks or loss of pressure.
  • Fluid Choice: Only use a high-quality coolant premixed with distilled water. Using tap water can cause mineral buildup and reduce cooling performance.
  • Regular Checks: As this model is vintage, inspect hoses, radiator, and seals at every coolant change for wear, swelling, or cracking.
  • Service Interval: Replace coolant at least every 2 years or sooner if discoloration or debris is present.

Keeping your 1978 Suzuki RM250's cooling system fresh is vital for reliability, especially for aggressive trail riding or racing. Attention to detail and proactive care will keep your classic RM250 running cool season after season.

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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.