Engine Oils
Background & Properties
castrol.com/GPS
800 255 4417
May 2025
GPS
Industry Specifications
History
Over the years, the drivers for change in diesel engine oils have been based upon the U.S. Environmental
Protection Agency (EPA) regulations for exhaust gas emissions. ese changes occur every few years. To be
able to meet ever- tightening limits, engine manufacturers must change engine designs; these design
changes almost always put additional stresses on the oil, therefore calling for new engine oil service
categories. With particulate matter (PM) and nitrogen oxide gases (NOx) already at very low levels, the newer
exhaust emission regulations address the reduction of greenhouse gases (GHG), especially carbon dioxide
(CO
2
). e CO
2
limit has led to the development of the next generation heavy duty (HD) engine oil for low GHG
engines. e first licensing of the new American Petroleum Institute (API) specifications, CK-4 and FA-4,
began on December 1, 2016.
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