The Complete Handbook of Vehicle Power Steering Fluid

Chapter 1: Understanding Vehicle Power Steering Fluid

Power steering fluid is a hydraulic medium. That simple statement contains most of what you need to know to understand why this fluid matters, and why misunderstanding it costs money.

A hydraulic system transmits force through an incompressible liquid. Your vehicle's power steering system uses this principle to amplify the force you apply at the steering wheel—multiplying your hand pressure by a factor of five to twenty, depending on the vehicle and steering ratio—and delivering that amplified force to turn the front wheels. Without that amplification, steering a vehicle, especially at low speeds or while parked, would require genuine muscular effort. With it, steering is effortless.

Power steering fluid is the medium that makes this work. It fills every passage in the pump, hoses, control valves, and cylinders. When you turn the steering wheel, you rotate a pump—either mechanically connected to the engine (older vehicles) or electrically driven (modern ones). That pump pressurizes the fluid. The pressurized fluid flows to a control valve that directs it to one side or the other of a steering cylinder or rack. The pressure pushes against a piston or spool inside that cylinder, which moves the steering linkage, which turns the wheels. The more precisely the fluid transmits that pressure, and the more stable it remains under the heat and stress of that pressure, the better your steering responds and the longer every component in the system lasts.

This is why power steering fluid is not commodity.