Power steering fluid

Power-steering fluid transfers hydraulic pressure from the pump to the steering gear, lubricates the pump and rack or box, carries heat and protects seals and metal surfaces. Some vehicles specify a particular automatic-transmission fluid; others require a dedicated mineral, synthetic or central-hydraulic fluid. Fully electric steering has no hydraulic reservoir, while electro-hydraulic systems still use fluid and a high-current pump.

Select only by the exact vehicle specification and approval, not colour or a broad “universal” claim. Confirm VIN, build date, steering system and pump type, required fluid standard, service temperature and compatibility with any shared suspension or brake-assist circuit. Red, green, amber and clear fluids can have unrelated chemistry, and dyes change with age.

Heavy steering, pump whine, foaming, low level, uneven assistance or wetness does not prove the fluid alone is at fault. Inspect hoses, crimps, cooler, reservoir/filter, pump drive, electric pump supply, rack boots, seals, steering joints, tyre pressures and alignment. A falling level indicates leakage; topping up repeatedly can hide a safety defect.

Work with the engine off and fluid cool unless the level procedure specifies another condition. Clean around the cap before opening, protect paint and wear eye/skin protection. Never add brake fluid, engine oil or an unapproved ATF. If the existing fluid is unknown or contaminated, do not mix experimentally; identify the system and use a controlled exchange or repair procedure.

Fill only to the correct hot or cold mark, then bleed by the vehicle method—often raising the front safely, turning slowly lock-to-lock with the engine off, then running briefly without holding against full lock. Electro-hydraulic systems may require diagnostics. Watch for bubbles, noise and leaks, recheck level after cooling and dispose of old fluid responsibly. Stop for sudden loss of assistance, hose bulging, fluid on exhaust or steering that binds. Vehicle-approved power-steering fluids are listed below.

Your Current Vehicle

Select Your Vehicle

Hydraulic steering fluid performs several jobs at once

The pump raises fluid pressure, the control valve directs it to one side of the steering piston and the reservoir accepts return flow. The fluid also lubricates vanes, bearings, seals and rack surfaces while transporting heat.

Viscosity, friction behaviour, anti-wear chemistry, oxidation stability and seal compatibility are all calibrated. Similar colour does not make fluids equivalent.

Steering-system types

System	Energy source	Fluid?	Service focus
Belt-driven hydraulic	Engine drives vane/gear pump.	Yes.	Belt, pump, hoses, reservoir and rack.
Electro-hydraulic	Electric motor drives hydraulic pump.	Yes.	Fluid plus high-current electronics/coding.
Hydraulic steering box	Engine/electric pump assists recirculating-ball box.	Yes.	Hoses, sector seals and adjustment.
Shared central hydraulic	Pump serves steering and other functions.	Yes, specialist.	Exact mineral/synthetic approval and bleed.
Electric power steering	Motor assists column or rack.	No steering fluid.	Electrical, sensors and mechanical joints.

Use the stated approval

“ATF” and “green fluid” are not specifications

Some older systems use a named Dexron-era ATF; others need low-viscosity cold-climate or central hydraulic fluid. Additive and base-oil differences affect seal swell, pump wear and low-temperature response.

Read reservoir cap, owner's information and current service data. Where sources conflict, resolve by VIN and component revision before filling.

Selection checklist

Check	Variation	Risk if wrong
Vehicle/build date	Mid-model pump/rack change.	Wrong viscosity or seals.
System type	Hydraulic, electro-hydraulic or shared circuit.	Filling a non-service point/wrong fluid.
Approval	OEM standard, not generic family.	Wear, noise and leakage.
Temperature	Cold-flow and hot viscosity needs.	Heavy cold steering or thin hot film.
Material compatibility	Hose and seal elastomers.	Swelling, hardening or leak.
Shared functions	Suspension, brake booster or fan hydraulics.	Multiple-system failure.

Symptoms and diagnostic direction

Symptom	Fluid-related possibility	Other checks	Urgency
Pump whine	Low level, air, wrong viscosity or contamination.	Pump wear, filter and hose restriction.	High.
Foam/milky fluid	Air ingress or mixed fluid.	Return below level, suction hose and seal.	Stop/bleed after repair.
Heavy steering	Low/incorrect fluid.	Pump, belt, electric supply, rack and joints.	Immediate if sudden.
Fluid dark/burnt	Oxidation/overheat or wear debris.	Cooler, pump and pressure.	Prompt.
Level falls	External/internal leak.	Hoses, rack boots, pump and cooler.	Immediate diagnosis.
Assistance changes hot	Viscosity/overheat/air.	Pump clearances and control valve.	High.

Checking the level correctly

Park on level ground, set wheels and engine state as specified and use the correct HOT/COLD marks, dipstick or electronic procedure. Wipe the cap area first. Overfilling causes aeration and overflow; underfilling exposes the pump pickup.

Do not infer level from reservoir staining or an opaque wall. Use the dipstick or service method.

Fluid condition

Compare a sample with fresh correct fluid in clean clear containers. Darkening can reflect age, but metallic sparkle, rubber debris, water or incompatible colour separation needs component investigation.

Odour and colour alone cannot prove viscosity or approval. Laboratory analysis may be appropriate after a major failure.

Common leak points

Area	Evidence	Repair direction
Reservoir/suction hose	Damp clamp, hard hose, air without large drip.	Renew hose/seals and bleed.
High-pressure crimp	Wet sleeve or spray under load.	Replace rated complete hose.
Pump shaft	Fluid behind pulley.	Assess pump and belt contamination.
Rack boots	Boot swollen with fluid.	Internal rack seal failure.
Cooler/pipe	Corrosion, impact or rub.	Renew and restore mounts.
Steering box	Sector/input seal wetness.	Repair/replace by approved method.

Air ingress can occur without a visible leak

The suction side operates below atmospheric pressure. A hardened O-ring or loose clamp can draw air inward but leak little fluid outward. Fine bubbles and pump whine after start are clues.

Inspect the complete pickup path and reservoir filter. Do not smear sealant over hose joints.

Pump drive and electrical supply

For belt pumps, inspect belt contamination, tensioner and pulley alignment. Fluid-soaked belts may need replacement. Do not overtension to hide a weak pump.

For electro-hydraulic pumps, test battery/charging voltage, high-current supply, earth, command and thermal codes. Low voltage can reduce assistance even with perfect fluid.

Pressure and flow testing

Use a rated hydraulic gauge and shut-off/flow tool in the named line. Follow maximum valve-closed time; dead-heading the pump rapidly overheats fluid and can burst hoses.

Compare idle and controlled rpm pressure, flow and temperature. Keep hands away from suspected high-pressure leaks.

High-pressure injection injury

A pinhole jet can penetrate skin and cause severe tissue damage. Never feel for a leak. Use shields, paper/approved detection at distance and depressurise before touching.

Any suspected injection injury is a medical emergency even if the puncture looks small.

Fluid exchange versus simple top-up

Top-up is appropriate only when the existing fluid is known, compatible and the cause of loss is corrected. An exchange replaces aged fluid but does not clean mechanical damage or cure leaks.

Power-flushing at uncontrolled pressure can damage systems. Use the vehicle's return-line, reservoir extraction or dedicated method and prevent the pump running dry.

Contamination after component failure

A failed pump can distribute metal through rack, hoses and cooler. Follow the repair scope for flushing or replacement; some coolers and racks retain debris and cannot be reliably cleaned.

Fit any reservoir/filter required and use clean dedicated equipment. A single particle can stick a control valve.

Safe preparation

Stage	Control	Prevents
Identify fluid	Confirm approval before opening.	Incompatible mixture.
Cool system	Allow fluid/engine to safe temperature.	Burns and false level.
Clean cap	Remove dirt around reservoir.	Valve/pump contamination.
Support vehicle	Use rated lift/stands for wheel-free bleed.	Vehicle fall.
Protect finish	Capture fluid and clean spills.	Paint, belt and floor damage.
Cap lines	Use clean hydraulic-compatible plugs.	Dirt and fluid loss.

Bleeding conventional hydraulic steering

With wheels raised if instructed, fill to cold mark and turn the steering slowly through its range with engine off, without holding at stops. Allow bubbles to settle and maintain level.

Start briefly, repeat at idle and monitor foam/noise. Some systems require vacuum filling or a specified front-axle load condition.

Do not hold full lock

At the steering stop, the relief valve opens and fluid heats rapidly. Holding full lock stresses pump, hoses and seals. Touch the stop only momentarily if the test procedure requires.

Increased noise at the stop alone is not a reason to add fluid.

Electro-hydraulic bleeding

Electric pumps can start with ignition or a door event and may need diagnostic activation. Follow safe power-down and voltage support. Do not run a dry pump continuously.

Calibrate steering angle or end stops where replacement procedures require.

Installation and refill controls

Check	Pass condition
Fluid	Exact approved product and clean batch.
Connections	New seals, natural alignment and torque.
Hoses	No twist, rub or exhaust contact.
Level	Correct mark at specified temperature.
Bleed	No foam, whine or level drop.
Function	Smooth assistance and no binding/leak.

Commissioning

Check steering from lock to lock without holding stops, observe assistance at parking and road speed and inspect pump, rack, hoses and cooler hot and cold. Recheck level after bubbles settle.

Confirm no belt slip, warning codes or unexpected current draw. Alignment and tyre pressures still affect steering effort.

Common mistakes

Do not choose by colour, mix fluids, use brake fluid, overfill, hold full lock, run pump dry, ignore leaks, power-flush blindly or put stop-leak in without explicit approval.

Stop-leak can swell seals and block small valves; it does not repair a split hose.

UK roadworthiness and environmental care

Sudden loss of steering assistance, binding or fluid on tyres/exhaust can make a vehicle unsafe and affect MOT. Hydraulic leaks contaminate roads and can create fire risk.

Capture old fluid and use an authorised waste route; never pour it into drains.

Practical power-steering-fluid FAQs

Q: Can fluid be chosen by colour?
A: No. Use the exact vehicle approval.

Q: Does every power-steering system use fluid?
A: No. Fully electric systems do not.

Q: Can ATF be used universally?
A: No. Only where the vehicle specifies that exact ATF standard.

Q: Why does the fluid foam?
A: Air ingress, low level, overfill or wrong fluid may be responsible.

Q: Can a leaking system just be topped up?
A: No. Find and repair the leak.

Q: Should steering be held at full lock?
A: No. It rapidly heats and loads the system.

Q: Can brake fluid be added?
A: Never. It can damage steering seals.

Q: Is dark fluid automatically failed?
A: It needs context; inspect odour, debris, approval and system condition.

Q: Can a pinhole leak be felt by hand?
A: No. High-pressure fluid can inject through skin.

Q: Does pump noise prove low fluid?
A: No. Air, restriction, wear and belt/electrical faults can cause it.

Q: Must electro-hydraulic systems be scanned?
A: Many require diagnostic activation, codes or calibration.

Q: Can stop-leak repair a hose?
A: No. Replace the failed component properly.

Q: How is bleeding complete?
A: Stable level, no foam/noise and smooth leak-free assistance.