How to Change the Coolant in a 1983 Honda CR125

Shop parts for a 1983 Honda CR125 Dirt Bike.

Changing the coolant in your 1983 Honda CR125 is a vital part of routine maintenance. This process not only helps keep the engine running cool but also extends the life of essential components. The 1983 CR125, a classic two-stroke motocross bike, relies on a liquid-cooled system – this means that fresh coolant is critical for maintaining top-level performance and preventing expensive failures from overheating. Below is a MotoSport-exclusive guide on how to change your bike's coolant with confidence.

Why Change the Coolant?

Fresh coolant does more than just prevent overheating. It improves heat transfer, discourages corrosion, and reduces the risk of internal deposits blocking narrow passages, all of which are important for the 1983 CR125's narrower, high-revving liquid-cooling system. For most riders, a coolant change every 40-50 hours of ride time (or once a season) is ideal*.

Tools & Supplies Needed

  • Fresh motorcycle coolant (never use pure water or automotive coolant)
  • Catching pan
  • 10mm wrench or socket
  • Flat screwdriver (for plastics or clamps, if necessary)
  • Funnel
  • Clean rags
  • New washer (recommended) for the coolant drain bolt
  • Gloves (coolant is toxic; avoid contact with skin)

Step-By-Step Coolant Change Process

  1. Allow the engine to cool completely. Never remove the radiator cap while the engine is hot, as the pressurized system may expel scalding coolant.
  2. Remove the seat and side panels as necessary to access the radiator cap and overflow tank, if equipped.
  3. Take off the radiator cap. Gently turn the cap counterclockwise to the first stop, allow any pressure to release, then remove completely.
  4. Place a catching pan under the water pump area (right side of the engine).
  5. Locate the coolant drain bolt. On the CR125, this is usually at the bottom of the water pump housing and will have a copper or aluminum crush washer.
  6. Loosen and remove the drain bolt with your 10mm wrench. Coolant will flow out quickly; let it drain fully.
  7. Kick the engine over a few times (with the kill switch depressed) to help empty the system.
  8. Reinstall the drain bolt with a new washer. Tighten it snugly, but do not overtighten—the water pump cover is aluminum and can strip easily.
  9. Check hoses and clamps. This is a good opportunity to inspect for cracks, leaks, or loose clamps.
  10. Pour fresh coolant into the radiator slowly, using a funnel. Fill until you see coolant at the bottom of the filler neck. If your bike has an expansion/reservoir tank, fill it to the "Full" mark.
  11. Reinstall the radiator cap. Make sure it's tight and properly seated.
  12. Start the bike and let it run for several minutes (watch for temperature). Gently blip the throttle to help circulate any trapped air. Shut off and let the engine fully cool, then recheck coolant level and top off if necessary*.
  13. Wipe up any spilled coolant and reinstall panels/seat.

Special Notes for the 1983 Honda CR125 Owner

  • The 1983 CR125 is a vintage machine with aluminum radiators and a small water pump. Always use coolant labeled safe for mixed-metal systems.
  • If you see persistent air bubbles or the coolant level drops after several heat cycles, inspect your head gasket or radiator for potential leaks.
  • Never use tap water – minerals can rapidly corrode the CR125's aluminum components. Use only distilled water if mixing a concentrate.
  • Coolant leaks, especially under the water pump, could signal a failing seal, a common issue as these bikes age. Address promptly to prevent transmission fluid & coolant mixing.
  • Dispose of drained coolant responsibly. Coolant is highly toxic and must not be poured into drains, storm sewers, or onto the ground.

Final Inspection & Tips

  • After the engine fully cools following your initial run, always recheck and top off the coolant as air will vent from the system as it's purged.
  • If you ride aggressively or in hot climates, consider a high-performance coolant for added protection.

Maintaining a clean, properly filled cooling system is key to keeping your 1983 Honda CR125 running great – from the local track to the vintage races. For replacement parts, radiators, hoses, and more, MotoSport has all you need to service your ride.

*Always consult your bike's service manual and our MotoSport guides for specific capacities and further tips tailored to the 1983 CR125.

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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.