How is hydraulic fluid made?
Most hydraulic fluid is basically an oil similar to kerosene but with special properties. In most cases it is non-flammable for safety reasons. It has good lubricity and low viscosity. Depending upon the application, there may be special additives added to control for high temperatures and compatibility with seals and other materials it may come in contact with. There are special refining processes involved in manufacturing it out of crude oil but it is about like 10 weight motor oil in nature and in some cases I know that 10W has been used as a substitute when the correct fluid was not available. Brake fluid in cars and trucks is a hydraulic fluid and in that case as it has contact with the air, and we don’t want water vapor dissolving into the fluid, it is usually hydrophobic (repels water).
