How to Change the Coolant in a 1978 Honda CR125
Shop parts for a 1978 Honda CR125 Dirt Bike.
Owning a vintage 1978 Honda CR125 is all about keeping it in peak form for the track or trail. One essential maintenance task is changing the coolant–vital for optimal engine performance and longevity. The early CR125s used a simple, efficient liquid-cooling setup but lacked some of the sophistication of modern bikes, so regular attention is crucial. Below you will find a detailed, MotoSport-exclusive step-by-step to refresh your CR125's cooling system.
What You Need
- New coolant (glycol-based, pre-mixed or mixed with distilled water)
- Drain pan
- Socket or wrench (appropriate size for drain bolt)
- Replacement copper or aluminum washer (recommended for drain bolt)
- Gloves & safety glasses
- Clean funnel
Coolant Change Procedure for 1978 Honda CR125
-
Prepare the bike.
Ensure the engine is cool to prevent burns. Place the bike upright on a stable surface or stand. -
Remove the radiator cap.
Release pressure in the cooling system by slowly removing the radiator cap. Never open when hot–risk of injury from pressurized steam or hot fluid. -
Locate and remove the coolant drain bolt.
Place a drain pan under the water pump (usually left side of engine case). Loosen the drain bolt–commonly found at the lowest point of the water pump cover. Some fluid will gush out quickly, so be ready.
Inspect the old sealing washer and replace it with a new one before reinstalling the bolt for a secure fit and to prevent leaks. -
Drain the coolant.
Allow coolant to drain completely. To ensure a full drain, gently lean the bike side-to-side or cycle the kickstarter by hand a few times–this helps remove stubborn fluid from engine passages. -
Reinstall the drain bolt and washer.
Securely reinstall the drain bolt with a fresh washer. snug tight, but do not overtighten–aluminum threads are soft and prone to stripping. 10 Nm torque is a good guideline. -
Refill the radiator with fresh coolant.
Using a funnel, slowly pour pre-mixed coolant up to the filler neck in the radiator. Slow pouring reduces air bubbles. Tap hoses gently to help trapped air escape. -
Prime and bleed the system.
With the filler cap off, start the engine and let it idle for 2–3 minutes. Blip the throttle a few times to circulate coolant and dislodge air pockets. -
Top off coolant and secure the cap.
Switch off the engine, allow it to cool, then check and top up the radiator if necessary. The fluid level should be right at the base of the filler neck. Reinstall and tighten the radiator cap securely.
Model-Specific Tips for the Vintage CR125 Owner
- Cooling system simplicity: The 1978 CR125 uses a basic radiator setup with minimal expansion tank volume. This makes the system more susceptible to air pockets–proper bleeding is especially important for vintage models.
- Watch for leaks: Over time, rubber hoses and seals can harden or crack. Inspect all connections. Replace worn or brittle hoses with quality aftermarket options available from MotoSport's 1978 CR125 parts lineup.
- Distilled water only: If mixing your own coolant, always use distilled water to avoid mineral deposits which can reduce cooling efficiency in the narrow water passages typical of older engines.
- Check frequently: Vintage bikes, especially those ridden hard, may require more frequent coolant checks and changes due to less efficient radiators and increased risk of leaks from age.
Final Checks
- Wipe up any spilled coolant–makes it safer for you and the environment. Dispose of old coolant responsibly.
- Monitor coolant level for several rides–top up as needed and watch for recurring drops (could indicate a slow leak).
- If overheating persists after a coolant swap, inspect the radiator and water pump for blockages or mechanical failure.
Stay ahead of overheating and protect your engine–regular coolant changes are essential maintenance for classic motocross bikes like the 1978 Honda CR125.
Related Shopping Categories
Shop Radiators for a 1978 Honda CR125 Dirt Bike.
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Shop Temperature Sensors for a 1978 Honda CR125 Dirt Bike.
Shop Tools for a 1978 Honda CR125 Dirt Bike.
Shop Radiator Hoses for a 1978 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.