What are the different grades of fully synthetic engine oil?
1 Answers
Currently, fully synthetic engine oils are primarily classified under the SN grade. The API (American Petroleum Institute) categorizes engine oils into grades SA, SB, SC, SD, SE, SF, SG, SH, SJ, SL, SM, and SN, with each subsequent grade representing a higher quality. The SN grade is currently the highest available. SJ was the standard in the 1990s, SL in 2001, SM in 2004, and SN in 2010. Semi-synthetic engine oils are mainly classified under SL, SM, and SN grades, with SN being the most common. However, fully synthetic oils represent the highest grade, exemplified by the SN level. The key differences between fully synthetic and semi-synthetic oils are that fully synthetic oils can operate over a wider temperature range, have a longer service life, and are more expensive. For the same oil film requirements, fully synthetic oils can achieve the desired performance with lower viscosity, whereas semi-synthetic oils require a relatively higher viscosity to meet the same standards. In identical working conditions, fully synthetic oils last significantly longer than semi-synthetic oils, making them more costly upfront. However, when considering the reduced frequency of oil changes, the overall cost is not significantly higher. There is no uniform standard for the color of fully synthetic engine oil. High-quality oil typically appears as a translucent yellowish-brown. If the oil turns brown, it may indicate the presence of water. After the engine has been running for a while, the oil may appear milky white with foam. Black oil usually suggests excessive sludge, iron particles, or carbon deposits. To check the oil's condition, pull out the dipstick and observe the markings against a light source. If the markings are not clearly visible through the oil on the dipstick, the oil is too dirty and should be replaced immediately.
