How to Choose the Right W Rating for Engine Oil?
3 Answers
Engine oil The method for selecting the W rating of engine oil is: For cold winters in the north, car owners can choose engine oil with a smaller number before the W, which provides better lubrication and protection during cold starts at low temperatures. For hot summers in the south, car owners can choose engine oil with larger numbers in the latter two digits, ensuring greater protection even when the engine overheats. Engine oil is a substance enhanced with additives in base oil, primarily containing anti-wear additives, detergents, dispersants, and multi-grade viscosity index improvers. Engine oil is used for lubricating internal combustion engines, with its main functions being to reduce friction and wear on moving parts and to remove sludge and varnish from the engine.
With over a decade of driving experience, I’ve learned that choosing the right oil W-rating is quite particular. Living in northeastern China where winter temperatures drop below -20°C, using a higher-viscosity oil like 10W-40 makes cold starts a struggle—the oil pump can’t circulate the thickened oil, leaving the engine sluggish until it warms up. In contrast, 5W-30 flows much smoother, ensuring reliable starts even in subzero conditions while protecting the engine. During summer’s wide temperature swings, the latter numbers (e.g., 30 or 40) indicate high-temperature protection: 30 suits daily driving, while 40 better handles high-speed runs or older engines prone to leaks. Always check your vehicle’s manual for the manufacturer’s recommendation—Toyotas often specify 5W-20, while German cars may call for 5W-30. Using the wrong grade risks accelerated wear and higher fuel consumption. When in doubt, consult a professional shop, and don’t neglect the oil change interval (typically yearly or every 10,000 km). Follow these simple steps for hassle-free maintenance and peace of mind.
When repairing a car, I first look at the W value of the engine oil to assess its low-temperature fluidity. The number before the W, such as 5W or 10W, indicates this property—the smaller the number, the better. For example, 5W oil can still run smoothly at -30°C, while 10W oil struggles, making it more suitable for warmer regions like Hainan. The numbers after the W, such as 30 or 40, represent high-temperature viscosity control. A 40-grade oil provides more stable lubrication in summer heat, better protecting internal components. It's also important to consider the API grade and SAE standards when choosing between full synthetic or semi-synthetic oil. Full synthetic oil offers stable viscosity, durability, fuel efficiency, and reduced oil consumption. Choosing the wrong W value can lead to increased engine noise or even black smoke. Beginners are advised to follow the manual rather than opting for cheaper options or blindly following trends. In regions where temperatures drop quickly, it's best to use a lower W grade like 0W-20. Regularly check the oil dipstick for color and change the oil promptly. Remember this simple rule: a smaller W number means better cold starts, and a larger number ensures stability at high temperatures.
