How are automotive engine oil grades classified?

[Delilah]

Automotive engine oils are divided into gasoline engine oils and diesel engine oils. The classification includes two aspects: quality grade and viscosity grade. For passenger cars, in regions like Northeast China, 5W-30 or 5W-40 is recommended, while in southern regions, 10W-40 or 15W-40 is suggested. Here is some relevant information about automotive engine oil: Quality grades of automotive engine oil: In terms of quality grades, the API (American Petroleum Institute) classification includes SA, SB, SC, SD, SE, SF, SG, SH, SJ, SL, SM, and SN grades. When selecting engine oil, it is essential to strictly follow the grade specified in the vehicle's user manual. If the same grade is not available, a higher grade can be used, but a lower grade should never be substituted. Impact of engine oil viscosity: The SAE viscosity classification for summer oils includes grades such as 20, 30, 40, and 50. The higher the number, the greater the viscosity, and the higher the maximum applicable temperature.

[RhettDella]

With 20 years of driving experience, I can tell you that oil grades depend on two key ratings. In the SAE viscosity rating, like 5W-30, the smaller the number before W, the smoother the cold starts, while higher numbers like 30 or 40 after the W indicate better high-temperature protection. Then there's the API classification with letter combinations like SN or SP - it's like smartphone OS updates where later letters mean newer technology. When I changed oil for my old Crown two years ago, I checked the manual: older cars can use SN grade, while newer models need SP-grade to keep up with technology. Some car enthusiasts think more expensive oil is always better, but actually it depends on vehicle age and driving habits - highway commuters and city drivers have completely different requirements.

[Lorenzo]

Last time I took my little Fit for maintenance, the mechanic pointed at the oil canister and taught me how to read the labels. In 5W-30, the W stands for winter, and the number 5 in front means it can start the engine even at -30 degrees Celsius, which is much better than 10W. The number 30 at the back relates to the oil film thickness at high temperatures, and 30 is just right for my small car, while my neighbor's SUV needs 40. The letter rating SP is one level higher than SN, mainly improving cleaning performance—engines with less carbon buildup won't act up. Remember this tip: for new Japanese cars, 0W-20 is usually the right choice, while older German cars need 5W-40 to be safe.

[BentleyAnn]

Last week, a Sylphy came into the repair shop because the wrong high-viscosity oil was used, causing oil pump damage. Currently, there are two sets of standards for oil grading: the SAE viscosity rating is like clothing—you need to choose the right size based on the engine's seasonal temperature differences. The API quality grade is like the freshness of ingredients; the SP grade has better phosphorus content control than SN, which can protect the catalytic converter for a few more years. The fully synthetic and semi-synthetic oils you often ask about are actually unrelated to the grade. The key is to check the certification number required in the owner's manual. For example, GF-6 certified oils come with anti-pre-ignition formulas, which are particularly friendly to turbocharged cars.

[VanWeston]

Confused by the string of codes on the engine oil bottle? Simply put, they indicate viscosity grade and quality grade. The SAE viscosity, like 0W-20, shows low-temperature fluidity with the number before W—0W outperforms 5W in northern climates. The 20 after refers to high-temperature protection; new cars typically use 20/30, while older cars are better off with 40. The API quality grade is more critical—SP grade adds oxidation stability tests over the older SN grade, extending oil life by 5,000 km. Don’t just pick oil by brand; check your owner’s manual first. My old Camry runs perfectly on 5W-30 SN-grade oil—upgrading to SP would be a waste of money.

[OBethany]

Remember being overwhelmed by the label parameters during my first oil change? It essentially boils down to two governing systems. The SAE viscosity grade dictates the operating temperature range—subtract 35 from the number before 'W' to get the minimum applicable temperature (e.g., 0W suits -35°C). The API service classification has evolved through 12 generations from SA to SP, with SP-grade specifically enhancing turbo protection, offering 10% more wear resistance than SN. Oil selection hinges on engine compatibility: SN suffices for naturally aspirated engines, while turbocharged models—especially those frequently used for long-distance driving—benefit most from SP-grade oils, as premium lubricants can save significant repair costs.