Power Steering Fluid and Hydraulic Systems

Hydraulic power steering systems — found on older vehicles and many trucks — use a belt-driven pump to generate hydraulic pressure. A rotary valve in the rack or gearbox directs that pressure to the appropriate side of a piston based on which way you are turning, multiplying your steering effort.

Low fluid or contaminated fluid causes almost every power steering noise and performance complaint. Check fluid level with the engine off — the reservoir has HOT and COLD marks. Use the correct specification fluid — power steering fluid, ATF, or synthetic depending on what the manufacturer requires. Using the wrong fluid damages seals and accelerates pump wear. Dark brown or black fluid with a burnt smell indicates the system has overheated and the fluid has broken down — flush and refill.

A whining noise that increases with engine RPM and gets louder when you turn the wheel is the power steering pump. Low fluid level is the first thing to check — air in the system from low fluid causes the pump to whine and foam the fluid. If fluid is full and correct, the pump is worn internally. Pump output pressure and flow testing against manufacturer specification confirms pump condition.

Hard to turn at all speeds — low fluid, failed pump, or broken drive belt. Hard to turn only at low speed and easy at highway speed — the pump may be producing enough pressure for highway driving but not enough volume for low-speed parking lot turns. Pump volume output drops as the pump wears. Hard to turn in one direction only — the rotary valve in the rack or gearbox is sticking or the rack has an internal seal failure on one side.