As a way to simplify oil classifications for the consumer, the oil industry has created a single "SG" classification. It will replace the dual classification, "SF-CC" previously used to indicate oils that meet the performance needs of newer model diesel and gasoline engines. In the past 10 years, the car engine has undergone many changes. As well as operating at higher temperatures, the smaller four, six and eight cylinder engines of the 1980s tend to rev higher. "SG" oils are best equipped to combat the sludge that develops in these engines.