There are different kinds of hydraulic fluids used in an automobile and they should not be mixed. Power steering fluid is the only hydraulic fluid that should be put in a power steering system.
Hydraulic fluids should be used according to manufacturer's instructions. They are designed and formulated for specific applications. For example, power steering fluid is appropriate for the rubber connections in the system.
Putting another hydraulic fluid in the power steering system can damage the rubber connections. In addition, a car manufacturer will often recommend using a power steering fluid specific for certain models.
Automatic transmission fluid and brake fluid are also used in automobiles and they are often made specifically for certain models. Hydraulic fluids also differ according to when they need to be replaced.
