How to Change the Coolant in a 1979 Honda CR125

Shop parts for a 1979 Honda CR125 Dirt Bike.

The Honda CR125 from 1979 is a classic motocross machine, prized for its responsive engine and lightweight chassis. Keeping your cooling system in top shape is vital to maintaining peak performance and longevity. Regular coolant changes help prevent overheating, corrosion, and premature component wear. Here–s a step-by-step guide tailored exclusively for your 1979 CR125.

What You Need

  • Fresh motorcycle-specific coolant (ethyl glycol-based; avoid automotive coolant with silicates)
  • Drain pan
  • Clean funnel
  • Wrenches for radiator cap and drain bolt
  • Distilled water (optional, for flushing)
  • Protective gloves & rags

Preparation

  • Ensure the engine is completely cool before starting. Hot coolant can cause severe burns.
  • Place your bike on a stable stand in a well-ventilated space.

Draining the Old Coolant

  • Remove the radiator cap by pushing down and twisting–never attempt this on a hot bike.
  • Set your drain pan under the water pump or coolant drain bolt, typically found at the lowest point of the right side engine cover.
  • Loosen and remove the drain bolt and allow all coolant to fully evacuate the system. Carefully dispose of the used coolant responsibly.

Flushing the System (Recommended for Older Bikes)

  • Reinstall and gently tighten the drain bolt.
  • Pour distilled water (or a 50/50 water and vinegar mix for extra cleaning power) into the radiator using your funnel.
  • Start the bike and let it idle for a minute, then shut off.
  • Remove the drain bolt again and allow the flushing solution to drain out. Repeat if the water runs dirty.

Refilling with Fresh Coolant

  • Reinstall and gently snug the drain bolt; don–t overtighten as these bolts can strip easily on older magnesium cases.
  • Slowly add fresh coolant into the radiator until it reaches the base of the filler neck. Listen for gurgling, and pause to allow trapped air to escape. Filling too quickly can trap air pockets.
  • Start the bike with the radiator cap off, let it idle, blip the throttle gently to help circulate coolant, then stop the engine.
  • Check the level–top off if needed, then securely reinstall the radiator cap with a firm twist until you feel the two positive “clicks.”

Final Checks

  • Clean any spillage from the frame or engine.
  • After your next ride, when the engine is cool, double-check the coolant level and add more if necessary.
  • Inspect for leaks, especially around the aging gaskets and drain bolt on these vintage bikes.

Important Notes for 1979 CR125 Owners

  • The 1979 CR125 uses a magnesium or aluminum engine case–never use automotive coolant with silicates, as it can corrode soft metals found in vintage bikes.
  • Check that all hoses and the radiator itself are free from cracks or bulges, as old components can fail under the new coolant pressure.
  • This model is known for a compact radiator and less robust cooling margin compared to modern bikes, so regular coolant changes are even more important, especially for riders pushing the bike hard or riding in warm conditions.
  • If you haven–t ever replaced the radiator cap, consider upgrading it to a modern pressure-rated cap to ensure a solid seal–pressure loss can cause overheating.

By staying proactive with coolant maintenance, your classic Honda CR125 will continue to deliver the throttle response and durability it–s known for on the track or trail. For OEM and aftermarket parts, shop parts for a 1979 Honda CR125 Dirt Bike.

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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.