Power Steering Fluid

Power steering fluid is the hydraulic fluid that transmits force through the power steering system on vehicles with hydraulic or electro-hydraulic power steering, enabling the power steering pump to assist the driver’s steering effort. It is stored in a reservoir typically located near the engine’s accessory drive belt, drawn by the power steering pump, pressurised to approximately 80–140 bar, and directed to the steering rack or steering box where it assists in moving the rack laterally in response to steering wheel input. Power steering fluid must withstand high pressure, high temperature from sustained steering effort (such as holding at full lock), and chemical attack from the aluminium, steel, and rubber components it contacts. Most vehicles use a manufacturer-specified fluid — either a dedicated power steering fluid or in some cases ATF — and these specifications are not interchangeable. Electric power steering (EPS), now standard on most new vehicles, eliminates the hydraulic system entirely and requires no fluid. Only vehicles with hydraulic or electro-hydraulic power steering systems require power steering fluid maintenance.

The power steering pump, driven by the engine’s serpentine belt, draws fluid from the reservoir and pressurises it. A rotary valve in the steering column senses the torque applied by the driver to the steering wheel and directs this pressurised fluid to the appropriate side of the steering rack’s hydraulic cylinder. The hydraulic pressure acts on the rack piston, generating an assisting force proportional to the driver’s input. When the steering wheel is centred and no torque is being applied, the rotary valve directs high-pressure fluid back to the reservoir with minimal resistance — the pump circulates fluid constantly but at low pressure. During parking or slow-speed manoeuvres where the highest assist is needed, the valve directs maximum pressure to the cylinder. The fluid must maintain consistent viscosity across operating temperatures and resist foaming from the cavitation that occurs when the pump operates near full lock — sustained full-lock operation is particularly demanding because the pump generates maximum pressure against a closed circuit, causing rapid heat buildup.

Power steering fluid leak: The most common power steering issue. Leaks develop at the pump shaft seal, the rack end seals, the high-pressure hose connections, or the reservoir outlet. Small leaks cause gradual fluid loss, eventual pump cavitation (a whining or groaning noise when turning), and ultimately pump seizure if the level drops critically low. Check the reservoir level and look for fluid staining on the pump body, hose connections, and at the rack boots at every service.

Contaminated or degraded fluid: Power steering fluid darkens and breaks down from heat cycling and oxidation, losing its anti-wear and anti-foam properties. Degraded fluid allows increased wear on the pump vanes and rack seals, contributing to the leaks described above. Foamy fluid (from air ingestion through a low-level condition) causes spongy, inconsistent steering response and pump noise.

Wrong fluid specification: Power steering systems are engineered to specific fluid viscosity and additive packages. Using ATF in a system requiring dedicated power steering fluid (or vice versa) causes seal swelling or shrinkage, changing the leak rate of all rubber seals in the system. Check the reservoir cap markings and owner’s manual before adding any fluid.

Level 1 — Monthly Level Check and Noise Monitoring: Check power steering fluid level monthly at the reservoir — most have MIN and MAX marks on the reservoir body. The correct level ensures the pump does not cavitate. Listen for whining, groaning, or squealing from the steering area when turning — these sounds indicate low fluid level, air in the system, or a failing pump. Any steering feel change — increased effort, inconsistent response, or vibration through the steering wheel — warrants immediate inspection.

Level 2 — Fluid Replacement Every 80,000 km or 5 Years: Replace power steering fluid preventively at this interval. Drain the old fluid from the reservoir with a turkey baster or hand pump, refill with fresh fluid, and cycle the steering lock-to-lock several times to flush the old fluid from the rack and return it to the reservoir; repeat until fresh fluid runs clear from the reservoir. Never hold the steering at full lock for more than a few seconds during this process as it overheats the pump.

Level 3 — Professional Inspection for Leaks: Any persistent power steering fluid loss requires locating the source before further topping up — adding fluid to a leaking system without repair allows the leak to worsen and can result in sudden complete loss of power steering assist, which significantly increases steering effort and can surprise a driver. Have the complete system pressure-tested to identify rack seals, pump seals, and hose failures.