What does SN or CF in engine oil mean?

[DeElliott]

SN in engine oil refers to the standard for gasoline engine oil, while CF refers to the standard for diesel engine oil. If the oil can is labeled with SN or CF, it indicates that the oil can be used in both gasoline and diesel engines, making it a universal type. Here, 'S' stands for suitability in gasoline engines, 'N' represents the highest grade for gasoline engine oil, 'C' denotes suitability in diesel engines, and 'F' signifies the highest grade for diesel engine oil. Engine oil, also known as motor lubricant, serves the following functions: 1. Lubrication and friction reduction; 2. Auxiliary cooling; 3. Sealing and leak prevention; 4. Rust and corrosion protection; 5. Shock absorption; 6. Cleaning and contamination removal.

[OTanner]

I usually pay attention to the letter codes like SN and CF when choosing engine oil. They are API oil quality classifications, where SN represents one of the highest grades for gasoline engine oils, suitable for most gasoline-powered cars today. CF, on the other hand, is a standard for diesel engine oils, but it's quite outdated now, as newer diesel vehicles typically use higher standards like CK-4. If gasoline-powered cars are mistakenly filled with CF-grade diesel oil, it may lead to issues like increased sludge and poor emissions. The oil packaging also displays viscosity parameters, such as the combination of numbers and letters like 5W-30, which is particularly important and must be matched according to the vehicle's maintenance manual. In short, when buying engine oil, first check the letter codes and then match them to your car's requirements to keep the engine in optimal condition.

[Peter]

I've seen plenty in repair shops, and I can tell at a glance what SN and CF on oil cans mean. SN is the top-tier standard designed for gasoline vehicles, with exceptional detergency and dispersancy to reduce sludge formation. Although CF is a diesel engine oil standard, it's basically obsolete for modern diesel engines, which now use newer standards like CJ-4/CK-4. If CF oil is mistakenly used in a gasoline engine, its anti-wear properties would be completely unsuitable, potentially causing damage to valve lifters over time. I remember a BMW owner once used the wrong oil, leading to a seized timing chain tensioner. So never compromise quality for price—always strictly follow the grade and viscosity specified in the owner's manual.

[CourtneyFitz]

When I first bought a car, I was also puzzled about what SN and CF in engine oil meant. Later, I learned that they are like the ID numbers of engine oil. SN is for gasoline engines, and the higher the number, the higher the grade. CF is for diesel vehicles, but newer diesel cars don’t use this grade anymore. When choosing engine oil, you shouldn’t just look at these letter combinations but also at the viscosity value like 5W-40 that follows. The most important thing is to flip to the last chapter of the user manual and find the oil specifications set by the manufacturer. If the manual specifies 5W-30 SN, then using 0W-40 SN would be incorrect. I’ve always bought oil according to the manual during maintenance, and my car’s engine remains very quiet even after 80,000 kilometers.

[BrielleMarie]

These letter grades essentially represent the performance certification system for engine oils. The SN grade is designed for gasoline engines, offering exceptional high-temperature cleanliness and effectively reducing carbon buildup in turbochargers. The CF standard serves as the basic specification for light-duty diesel engine oils, with relatively lower requirements for acid resistance. Nowadays, the SP grade has replaced SN, showing significant improvement in resisting low-speed pre-ignition. For average car owners, adhering to their vehicle manufacturer's certification standards is more straightforward. OEM-specific certifications like VW502/505 or MB229.5 prove more reliable than solely relying on API classifications. The most obvious symptom of incorrect oil selection is a ticking noise during cold starts, indicating insufficient oil supply to hydraulic lifters.