How to Change the Coolant in a 1979 Yamaha YZ250: A MotoSport Guide
Shop parts for a 1979 Yamaha YZ250 Dirt Bike.
Changing the coolant in your 1979 Yamaha YZ250 is crucial for maintaining optimal engine performance and longevity. This legendary bike, revered for its air-cooled two-stroke power and competition heritage, relies on a properly maintained cooling system for consistent performanceespecially important for vintage motocross machines. Below is MotoSport's proprietary guide tailored specifically to the unique requirements of your classic YZ250.
What Makes the 1979 YZ250 Unique?
The 1979 model year marked significant progress in Yamaha's motocross engineering. While many YZ250s up to the early 1980s were air-cooled (with radiators appearing on later models), some special or modified '79s may have liquid cooling. The basic principle remains: if your bike is fitted with a radiator and coolant systemfactory or aftermarketregular coolant changes are vital to protect aluminum and magnesium engine components from corrosion. If your YZ250 is strictly air-cooled as per Yamaha's original design, radiator and coolant service are not required; always verify your machine's setup before proceeding.
Tools and Materials Needed
- High-quality ethylene glycol-based coolant (with anti-corrosion properties for aluminum engines)
- Soft or distilled water (if mixing coolant)
- Socket set or wrench (for drain bolt removal)
- Drip pan or suitable container
- Rags or towels
- Protective gloves and eyewear
Step-by-Step Coolant Change Procedure
- Preparation
Allow the engine to cool completely. Never open the radiator cap when the engine is hot to avoid scalding injuries and system overpressure. - Position the Bike
Stand the YZ250 upright on a level surface. Remove the seat or bodywork panels as needed to access the radiator cap and drain bolt. - Drain the Old Coolant
Place a drip pan under the engine. Remove the radiator cap by turning it slowly to the detent to release any residual pressure. Then completely remove the cap.
Locate and remove the coolant drain bolt (typically at the bottom of the cylinder or radiator). Allow the coolant to fully drain into the pan.
Clean up any spills immediatelycoolant is toxic and can damage painted surfaces. - Flush the Cooling System
After draining, reinstall the drain bolt temporarily and fill the radiator with clean tap water. Reinstall the cap and start the bike for a brief idle (just a few moments, not allowing it to heat up fully), then turn it off.
Remove the drain bolt again and drain the system completely to flush out debris or old coolant. - Refill with Fresh Coolant
Reinstall the drain bolt with its copper washer and torque to spec (typically around 10 Nm). Prepare a 50/50 mixture of high-quality coolant and soft/distilled water unless you use pre-mixed coolant.
Slowly fill the radiator to the recommended levelavoid air pockets by gently rocking the bike side to side.
Leave a small air gap in the radiator to allow for expansion. - Bleed and Recheck
With the cap still off, start the engine and let it idle for a few minutes; watch for bubbling, which indicates trapped air escaping. Top off coolant as needed. Reinstall the cap securely.
Check for any leaks at the drain bolt and hoses. - Dispose of Old Coolant Responsibly
Used coolant is hazardousnever pour it down the drain or on the ground. Take it to a local recycling or hazardous waste disposal facility.
Additional Maintenance Advice for the 1979 YZ250 Owner
- Avoid hard or mineral-rich water. Only use distilled or soft water when mixing coolant to prevent mineral buildup and corrosion in aging systems.
- Inspect hoses and radiator regularly. Given the age of the YZ250, cracked hoses or corroded radiator cores are commoninspect carefully during coolant changes.
- Coolant change interval: Replace coolant every two years or sooner with frequent racing or extreme use.
- If your model remains air-cooled, keep cooling fins clean and free of debris for best performance and avoid unnecessary coolant service.
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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.