How to Classify Engine Oil Grades?
3 Answers
Engine oil grades are typically classified by two methods: viscosity classification and oil quality classification. I. SAE Viscosity Classification: 1. High-temperature type for summer: 20, 30, 40, 50. The larger the number, the higher the viscosity, indicating suitability for higher maximum temperatures. 2. Low-temperature type for winter: 0W, 5W, 10W, 15W, 20W, 25W. The letter W stands for Winter, and the smaller the number before W, the lower the low-temperature viscosity and better low-temperature fluidity, indicating suitability for lower minimum temperatures. 3. All-season type for both winter and summer: 5W-20, 5W-30, 5W-40, 5W-50, 10W-20, 10W-30, 10W-40, 10W-50, etc. The smaller the number before W, the lower the minimum temperature the oil can withstand, and the larger the number after the hyphen, the higher the maximum temperature the oil can withstand. II. API Engine Oil Quality Classification: 1. Oils starting with S: SA, SB, SC, SD, SE, SF, SG, SH, SJ, SL, SM, SN. These oils start with S, and the letters range from A to N. Each subsequent letter represents a higher grade than the previous one. For example, SN is a higher grade than SM. 2. Oils starting with C: CA, CB, CC, CD, CE, CF. These are general-purpose diesel engine oils, and their letter grades are similar to S-grade oils. The later the letter in the alphabet, the higher the oil grade.
I've been driving for over a decade and know quite a bit about motor oil grading. It's mainly classified by viscosity and quality standards. First, let's talk about viscosity. Labels like 5W-30 and 10W-40 are established by SAE. The number before the W indicates cold-start fluidity—the lower the number, the easier it is to start. The number after represents high-temperature protection capability—the higher the number, the thicker the oil. For quality standards, there are API ratings like SN and SP. The higher the letter, the better the oil is at anti-wear, cleaning, and even fuel efficiency. I remember when I first changed my oil, I didn't understand and chose a lower grade, which resulted in louder engine noise. Later, I checked the manual and learned that new cars perform better with low-viscosity oils like 0W-20, while older cars are better suited for high-viscosity oils like 5W-40. The grading system exists to meet different engine needs. Don't underestimate it—using the wrong oil can increase fuel consumption and even damage the engine over time.
When working at the auto repair shop, I often help car owners choose engine oil. The grading depends on two aspects. For viscosity ratings like 5W-30, the number before W indicates better cold-start performance when smaller, while the larger number after shows better high-temperature protection - that's how the SAE standard works. For quality standards like API SP or CK-4 (for diesel), SP is the latest gasoline standard emphasizing environmental protection and fuel efficiency. Don't just look at price when selecting oil; consider your vehicle's requirements. For long-distance driving, full synthetic high-grade oil is recommended, while semi-synthetic works for urban short trips. I've noticed some people misuse high-viscosity oil, thinking thicker is always better, only to end up with an overburdened engine. The grading system enables more precise selection, reducing repair headaches.
