How to Change the Coolant in a 1974 Honda CR125: MotoSport Service Guide
Shop parts for a 1974 Honda CR125 Dirt Bike.
Keeping your 1974 Honda CR125 running strong comes down to routine maintenance–and few things are as critical as changing the engine coolant. The original CR125 is a legendary motocrosser, renowned for its light weight, simple construction, and race-bred two-stroke powerband. While its air-cooled engine means there's no modern radiator setup, some owners install aftermarket liquid-cooling systems for better performance. If your CR125 features a liquid cooling conversion, or you're referencing another vintage CR125 build with a radiator, this guide covers the proper steps for a robust coolant change.
Unique Notes on the 1974 CR125
- The 1974 Honda CR125M Elsinore left the factory as an air-cooled two-stroke, using cylinder fins to dissipate heat. There is no stock liquid-cooling or radiator system fitted from the factory.
- If your 1974 CR125 has been upgraded with an aftermarket liquid-cooled cylinder or head, follow these steps. For stock setups, regular cylinder fin cleaning and engine cooling maintenance are all that's required.
Tools & Supplies Needed
- Coolant catch pan
- Fresh ethylene glycol-based coolant
- Distilled water (if diluting concentrate)
- Screwdrivers/wrenches (for drain bolt, radiator cap)
- Gloves and rags
Step-by-Step Coolant Change Process
- Let It Cool. Ensure the engine is completely cool before starting. Opening a hot system can cause burns and messes.
- Remove the Radiator Cap. Locate and unscrew the radiator cap (or the cap on the highest point of the cooling system) to release pressure and allow air in, letting coolant drain freely.
- Locate the Drain Bolt. Most liquid-cooled conversions place a drain bolt on the lower side of the water pump or bottom of the radiator:
- Place a catch pan underneath.
- Carefully loosen and remove the drain bolt. Coolant will flow out quickly–avoid splashing.
- Flush If Necessary. For a thorough service, you can pour a small amount of distilled water into the radiator and replace the cap. Kickstart the engine several times to help clear out old coolant and loosen debris–then drain fully.
- Replace Seals and O-Rings. Inspect the drain bolt washer and radiator cap seal. Replace any worn items to avoid future leaks.
- Reinstall Drain Bolt. Secure the drain bolt back into place, snug but not over-tightened. Overtightening can damage threads or strip the casting.
- Refill Coolant. Use a funnel to pour new coolant up to the filler neck. A pre-mixed, motorbike-specific ethylene glycol coolant is best for aluminum radiators and modern conversions.
- Bleed the System. With the bike upright, gently rock it side to side to help air bubbles rise. On some systems, you may need to loosen a small bleed screw to let trapped air escape as you top off coolant.
- Run the Engine Briefly. Reinstall the radiator cap. Start the engine and allow it to run for a minute or two. Shut it off, let it cool completely, and recheck the coolant level. Add more coolant if needed to fill to the specified level.
Model-Specific Reminders
- The original 1974 CR125's legendary performance relies on diligent care. If you're running a stock air-cooled engine, keep cooling fins clean and unobstructed for best heat dissipation.
- Liquid-cooling conversions should have hoses, clamps, radiator, and water pump inspected regularly for leaks or corrosion.
- Replace coolant at least once per year or every 40–50 hours of ride time for best results.
Keep Your Elsinore Ready with MotoSport
With every coolant change, consider inspecting or replacing hoses, clamps, cap, and gaskets for trouble-free performance. Find everything you need to keep your classic 1974 Honda CR125 in race-ready shape at MotoSport.
Related Shopping Categories
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Shop Radiator Hoses for a 1974 Honda CR125 Dirt Bike.
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.