How to Change the Coolant in a 1973 Honda CR125
Shop parts for a 1973 Honda CR125 Dirt Bike.
The legendary 1973 Honda CR125 is an iconic machine–Honda's first two-stroke motocross bike and revered for its simplicity and performance. Like all vintage motorcycles, proper cooling system maintenance is vital for engine longevity and reliability. While this bike uses a relatively straightforward liquid-cooling system for its era, it's still important to change the coolant regularly or whenever the system is serviced. Below are step-by-step instructions unique to MotoSport for changing the coolant on your 1973 Honda CR125, along with tips specific to this classic dirt bike.
Key Considerations Before You Start
- Coolant Type: Use a glycol-based coolant designed for motorcycles, or distilled water with a coolant additive formulated for aluminum engines. Never use plain tap water as minerals can cause deposits and corrosion over time.
- Preparation: Always perform this service when the engine is completely cool to prevent burns and proper draining.
- Vintage Parts Alert: Given the age of this bike, inspect hoses and the radiator for cracks or leaks. Replace any worn gaskets or seals during the process for optimal results.
Step-by-Step: Changing the Coolant
- Remove the Seat and Side Panels (if needed)
To access the radiator cap and drain bolt, remove any necessary bodywork. On the CR125, access is typically straightforward. - Locate and Remove the Radiator Cap
Unscrew the cap from the radiator. This allows air to enter and helps the coolant drain more efficiently. – Be careful as pressure may still exist in the system. - Drain the Coolant
Locate the drain bolt at the bottom of the water pump. Place a catch pan underneath, then completely remove the bolt. Removing this bolt–along with the radiator cap–will ensure the system drains quickly.
Pro Tip: Removing any lower hoses can further speed up draining if your system is stubborn. - Inspect & Clean
Examine the drained fluid for any rust, debris, or oil–which can signal internal issues. Wipe the drain bolt clean and check or replace the washer/copper crush seal if necessary for a leak-free reinstallation. - Reinstall the Drain Bolt
Tighten the bolt securely. If your manual specifies, torque it to approximately 10 newton meters for an optimal seal.
Vintage tip: Many 1973 CR125s benefit from new copper or fiber washers; old, flat washers are notorious for slow leaks. - Fill with Fresh Coolant
Slowly fill the radiator with your chosen pre-mixed coolant or a 50/50 mix of coolant and distilled water until the fluid reaches the base of the filler neck. Avoid overfilling.
Wiggle or gently rock the bike to help release any trapped air while filling. - Burp the System
With the radiator cap still off, briefly start and run the engine at idle. As the coolant circulates, air bubbles will rise to the surface. Watch the level, top off as needed, then turn off the engine.
This step is critical on vintage models–air pockets can cause overheating. - Replace the Radiator Cap
Reinstall the cap securely. Wipe up any spills. - Check for Leaks and Reinstall Bodywork
Visually inspect for any drips around the drain bolt, hoses, and radiator seams. If all is dry, refit the seat and side panels. - Test Ride and Recheck
Briefly ride the bike and allow it to cool fully. Double-check the coolant level in the radiator. Add fluid if necessary and ensure the system remains leak-free after a full heat cycle.
Additional Tips Unique to the 1973 Honda CR125
- Original Radiator Design: Early CR125 radiators are unique and can be delicate. Keep fins clean and straight; bent fins reduce cooling efficiency.
- Cooling System Upgrades: Some owners fit aftermarket or reproduction radiators for better cooling–ideal for restored bikes ridden hard or raced.
- Service Interval: Replace coolant at least once a year, after any major engine work, or whenever the coolant appears dirty. Old coolant breaks down, risking overheating and corrosion.
Regularly servicing your vintage Honda's cooling system keeps your classic running cool & reliable. Explore performance-radiator caps, fresh hose kits, and quality coolant additives at MotoSport to protect your 1973 Honda CR125 for seasons to come.
Related Shopping Categories
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Shop Radiator Hoses for a 1973 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.