How to Identify Motor Oil Grades?
3 Answers
On the outer packaging of motor oil, you can find the SAE and API labels. SAE stands for the Society of Automotive Engineers, while API stands for the American Petroleum Institute. The grade following SAE indicates the viscosity value of the oil, and the grade following API indicates the quality level of the oil. Below is a detailed introduction: 1. SAE Classification: SAE-classified oils are generally labeled as 0W-20, 0W-30, 0W-40, 5W-20, 5W-30, 5W-40, 5W-50, 10W-20, 10W-30, 10W-40, 10W-50, etc. 2. API Classification: API-classified oils are divided into two types, those starting with S and those starting with C. S represents gasoline engine oils, with specifications including: API SA, SB, SC, SD, SE, SF, SG, SH, SJ, SL, SM, SN. C represents diesel engine oils, with specifications including: API CA, CB, CC, CD, CE, CF, CF-2, CF-4, CG-4, CH-4, CI-4.
Last time I helped a friend choose engine oil, I specifically researched the viscosity grade issue. The oil grade, like 10W-40, is a combination where the number before the W represents winter low-temperature fluidity - the smaller the number, the smoother cold starts will be. For example, 0W remains fluid even at -30°C. The 40 after represents high-temperature viscosity - during high-speed driving, the oil needs to be sufficiently thick to protect the engine. When changing oil, you must check the maintenance manual requirements. Japanese cars commonly use 0W-20, while German cars mostly use 5W-40. Choosing the wrong grade may increase fuel consumption or accelerate wear, especially for older cars where blindly using low-viscosity oil can actually lead to oil burning. Nowadays, full synthetic oils cover a wider range of grades, and their winter cold starts are noticeably smoother than mineral oils.
Based on my years of driving experience, the SAE rating on the oil container is crucial. The number before the letter W indicates low-temperature performance; for example, 5W is more cold-resistant than 10W. The number after the dash represents high-temperature protection capability. A viscosity of 30 is sufficient for city commuting, while a 40 is better for frequent long-distance driving. Friends in the north must pay attention to the number before W in winter—using 0W in sub-zero regions ensures smooth cold starts without engine strain. If you notice the old oil is too thin during an oil change, consider switching to a higher viscosity rating. However, if the engine is leaking oil, you should actually reduce the viscosity. Many repair shops now have viscosity reference charts—if unsure, simply provide your car model for them to check, which is the safest approach.
