How to Change the Coolant in a 1987 Honda CR125: Step-by-Step Guide

Shop parts for a 1987 Honda CR125 Dirt Bike.

Performing regular coolant changes on your 1987 Honda CR125 is essential for optimal engine performance, protection from overheating, and extending the life of the cooling system. Though the CR125 is a proven two-stroke contender, older models like this also come with age-related nuances – ensure every maintenance step is meticulous. This robust guide from MotoSport walks you through the entire coolant change process, along with tips specific to your CR125.

Why Coolant Changes Matter for Your 1987 CR125

Coolant degrades over time, losing its ability to regulate engine temperature and protect against corrosion. For vintage machines, old or contaminated coolant can mean costly repairs or even catastrophic engine failure. The 1987 CR125's aluminum cylinder head and water-cooled design demand fresh, high-quality coolant for consistent performance – especially under high-rpm riding.

Tools & Supplies You'll Need

  • Philips/flathead screwdrivers
  • 8mm and 12mm wrenches or sockets
  • Catch pan/container
  • Radiator flush (optional, recommended for neglected systems)
  • Fresh coolant (use motorcycle-specific, aluminum-safe coolant or a 50/50 premix with distilled water; avoid tap water to prevent mineral deposits)
  • Funnel
  • Shop towels
  • Crush washer for drain bolt (replace if worn)
  • Gloves and eye protection

Step 1: Prep the Bike & Work Area

  • Let your CR125 cool completely. Hot coolant is hazardous.
  • Stand the bike upright and remove the seat and tank shrouds for clear access to both radiators – using 8mm and 12mm tools as needed.

Step 2: Drain Old Coolant

  • Place the catch pan under the water pump cover (right side of engine, bottom of radiator hose).
  • Remove the radiator cap. This releases pressure for faster draining.
  • Locate the coolant drain bolt on the water pump – typically an 8mm or 10mm bolt. Loosen and remove it. Let the system drain completely. Inspect and replace the crush washer if needed for a proper seal.
  • Squeeze radiator hoses with your hand to help push out trapped coolant. You can remove the lower hose clamps if you want to inspect hoses for wear or additional draining.

Step 3: Optional – Flush the Cooling System

  • If the coolant appears rusty, oily, or debris-filled, fill the radiators with a flush solution or distilled water.
  • Reinstall the drain bolt, start the engine, and let the bike idle for a few minutes to circulate the flush.
  • Shut off, re-drain, and repeat until the fluid runs clear. Remove flush solution completely before refilling.

Step 4: Refill with Fresh Coolant

  • Reinstall and tighten the drain bolt with a new or inspected crush washer.
  • Slowly pour the new coolant into the radiator via the filler neck, using a funnel to prevent spills. Fill until the coolant reaches the base of the filler neck.
  • Check for leaks at the drain bolt, hose clamps, and water pump seam.

Step 5: Bleed the System & Check for Air

  • With the radiator cap off, start the bike and let it idle for 1–2 minutes. Squeeze the radiator hoses to encourage trapped air to rise.
  • Watch for air bubbles at the filler neck. Once they stop, the system is purged.
  • Shut off and let the bike cool, then top off coolant if needed so it remains at the filler neck base.
  • Reinstall the radiator cap securely.

Step 6: Final Level Check

  • Start the engine, bring to normal operating temperature, and check for leaks.
  • Let the bike completely cool – recheck coolant level in both the radiator and (if equipped) overflow reservoir. Top off as needed.
  • If checking again after your next ride shows a drop in level, repeat the air bleeding process; minor adjustments are normal for the first heat cycles.

CR125 Owner Tips – What to Watch For

  • Aluminum-specific coolant is best for the 1987 CR125's alloy cylinder and head. Avoid silicate-heavy car coolants. Distilled water with an additive is ideal.
  • Check radiator hoses and clamps for brittleness – old CR125s may have tired rubber prone to leaks.
  • If you see repeated loss of coolant without visible leaks, you may have a failing water pump seal or a head gasket issue. Inspect and address immediately to prevent engine damage.
  • Flush every 1–2 years, more often if racing or riding in harsh conditions.

Keeping your 1987 Honda CR125's cooling system maintained allows you to keep riding with confidence – from vintage race tracks to your favorite trails. For OEM and performance coolant system parts, gaskets, and tools, visit MotoSport for your CR125's next upgrade.

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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.