What do CF-4 and 15W-40 mean?

[SebastianLee]

CF-4 is the quality grade of automotive engine oil. Gasoline engine oils are classified as: SE, SF, SG, SH, SJ, SL, SM, etc. The further the letter after 'S' is in the alphabet, the better the oil. Diesel engine oils are classified as: CC, CD, CE, CF, CF-4, CH-4, CI-4, etc. For the comprehensive performance of the oil in terms of wear resistance, oxidation prevention, carbon deposit prevention, and fuel economy, from left to right, the higher the grade of the oil, the better its performance. 15W-40 is the viscosity grade of automotive engine oil, which includes: 5W-50, 10W-30, 15W-40, etc. These grades indicate all-season performance. The greater the difference between the numbers before and after 'W', the wider the applicable temperature range.

[AaliyahMarie]

I've been repairing cars for over a decade, and I frequently encounter specifications like CF-4 and 15W-40. CF-4 is an API (American Petroleum Institute) standard specifically designed for high-performance diesel engines, offering resistance to high-temperature wear and preventing carbon buildup. 15W-40 refers to the viscosity grade: 15W means the oil flows like a thin fluid at around -20°C for cold starts, while 40 indicates it maintains a thick oil film at 100°C to prevent engine friction. This oil is particularly suitable for trucks and older diesel vehicles, improving engine responsiveness and extending lifespan. However, in extremely cold regions, it may thicken and cause starting difficulties, so it's best used within a temperature range of -15°C to 40°C. When changing oil, I recommend checking the manual to select the correct grade—using the wrong one could damage components, which isn't worth the risk.

[MasonDella]

I often enjoy honing my driving skills, and CF-4 and 15W-40 are common in my toolbox. CF-4 is a classification indicator for diesel engine oil, meaning it can handle heavy loads and emission standards while keeping the engine internals clean. 15W-40 refers to viscosity parameters—15W makes it easier to start the engine in winter, reducing wear, while 40 ensures stable sealing at high speeds to prevent oil leaks. Using this oil in a diesel SUV delivers smooth performance with less noise and better fuel efficiency. However, keep in mind that in extremely cold winters, it may not start as easily as oils with a lower W rating. Understanding oil grades helps with routine maintenance and keeps your car running longer.

[AdrianaDella]

I just bought a car and learned from the mechanic that CF-4 is a diesel engine oil standard designed for heavy-duty vehicle engines. 15W-40 indicates the viscosity, with 15W ensuring quick starts in cold weather and 40 providing strong protection in hot conditions. This type of oil is suitable for daily use in trucks, but it's important not to use it in gasoline vehicles to avoid problems.