Does the American Petroleum Institute (API) set standards for the viscosity of all engine oils?

The American Petroleum Institute (API) does not set standards for the viscosity of all engine oils, which makes the selection of 'no, it does not cover all engine oils' accurate. The API primarily focuses on establishing standards for specific categories of engine oils based on performance and quality rather than setting universal viscosity standards for every type of engine oil available in the market.

API standards are categorized for different types of engine oils, including those for gasoline engines, diesel engines, and other applications. However, these categories do not encompass every possible formulation or blend of engine oil. Therefore, while the API does provide critical guidelines regarding the performance and specifications of many engine oils, it does not ensure that these standards apply universally to all engine oils available, especially niche or less common formulations that may exist outside of these defined categories.