So what is power steering fluid? Power steering fluid is hydraulic oil for the most part, with certain additives that are tuned for the automotive applications, but it is hydraulic fluid. In other words, you have a pump that creates pressure and that force is changed into energy at a steering rack by turning the wheels or extending the tie rods in either direction. What else is hydraulic on the vehicle? The automatic transmission. This is why some vehicles will actually specify transmission fluid to be used inside the power steering system, but there are exceptions. Certain vehicles out there, mostly Asian, have their own formulation of power steering fluid. So it is absolutely critical that you match the power steering fluid with the application. Some may use a different weight of oil, and if you use the wrong power steering fluid, it can change the feel of the steering, but most of all, it can damage the pump and the rack on the vehicle.