What Do Engine Oil Codes Mean?

[VonTravis]

The meaning of engine oil codes is as follows: Engine oil codes are divided into two categories, one is the oil viscosity, and the other is the oil grade. (1) Viscosity index: Generally, the SAE standard is used as the international standard, which is what we commonly refer to as 5W-20, 5W-30. The specific meanings are: The first number represents the low-temperature viscosity index, indicating the minimum working temperature at which the oil can function. (2) Grade index: In China, the API standard is generally used, divided into API SA, SB, SC, SD, SE, SF, SG, SH, SJ, SL, SM, SN, SP; Those starting with the letter "C" represent oils for diesel engines, with specifications including: API CA, CB, CC, CD, CE, CF, CF-2, CF-4, CG-4, CH-4, CI-4. If both are present, such as SM/CF, it indicates that the oil is suitable for both gasoline and diesel engines. This involves the oil's quality, shelf life, impurity content, etc. The later the grade, the higher the level, the better the quality, and the more expensive it is. This is what is commonly referred to as the standard for full synthetic and semi-synthetic oils. Generally, oils before SL are mineral oils, SM is semi-synthetic oil, SN and above are full synthetic oils, with the current highest grade being SP. Additionally, the European ACEA (European Automobile Manufacturers' Association) has established another set of standards, which are more stringent.

[MacDeclan]

I did some research on this when choosing engine oil before. The oil codes like '5W-30' are actually quite scientific with their letter and number combinations. The 'W' at the beginning stands for winter, indicating low-temperature performance; the smaller the number before it, the smoother the cold starts. When I lived up north, I used 0W oil, and it started fine even at minus twenty degrees. The number after, like '30', is the high-temperature viscosity index – if you're doing long highway drives in summer, a higher number protects the engine better. You should check your car's manual for recommendations. My old Japanese car uses 30, while my friend's German car requires 40. The additive formulas vary between codes too, and the difference in performance under high-temperature, high-load conditions is quite noticeable.

[MacAlina]

The repair shop guy explained the meaning of motor oil labels to me. Simply put, it's divided into three parts: The number before the W indicates low-temperature performance - the smaller the number, the better the low-temperature fluidity. New cars generally use thinner oils like 0W-20. The number after W relates to high-temperature protection - German turbocharged cars often use higher viscosities like 40 or even 50. Letters like SN and SP represent API quality grades, with the latest SP grade offering better turbo protection. I've seen cars using wrong viscosity grades during repairs - their cold-start noise sounded like tractors. It's best to follow the manufacturer's manual, as mixing different grades can disrupt additive balance.

[John]

Let's talk about some engine oil knowledge for girls~ The code like 5W-30 printed on the bottle is super practical. The W stands for suitable for winter use, with 5W flowing normally at -30°C, while my bestie's car in the south only needs 10W. The number 30 afterwards is like a sunscreen index—the higher the number, the thicker the oil, making it more reassuring for summer road trips or off-roading. Always check the manual when choosing; sedans usually use 20/30, while SUVs need 40 or above. Last time I picked the wrong grade, and fuel consumption shot up by over a liter.

[SanStella]

A mechanical engineer friend who specializes in engine oil told me that the code represents the SAE-certified viscosity standard. The key is to observe the relationship between the numbers before and after the 'W': for example, 0W-20 is an energy-saving type with good low-temperature fluidity but thinner at high temperatures, suitable for Japanese hybrid vehicles; while 5W-40, with its stronger high-temperature viscosity, offers better protection for older car engines. The differences between American and European standards mainly lie in the test temperatures, with North American vehicles commonly using oils with better low-temperature performance. The replacement cycle is also influenced by the code, as full-synthetic high-grade oils can last over 10,000 kilometers.

[LeMadison]

Experienced Road Trip Driver's Advice: Engine oil grades directly affect vehicle performance. Learned this the hard way on the Sichuan-Tibet route - must use 0W-grade at high altitudes for quick cold starts. Desert sections require high viscosity 40/50 grade, otherwise high-temperature oil film failure can cause cylinder scoring. Among common grades, 5W-30 is most versatile for varied climates. Pay special attention to the first letter quality rating - never use outdated SL-grade or older specs. Once made an emergency stop at a service station and mistakenly used SAE 20 - could hear the engine trembling during mountain climbs.