How To Get Air Out Of Power Steering: A Professional System Bleeding Guide

Eliminating trapped air from a hydraulic power steering system requires a systematic process of cycling the steering rack to displace air pockets into the reservoir. By utilizing manual cycles with the engine off or employing a vacuum pump, technicians can resolve cavitation-induced whining and erratic steering response while preventing long-term pump damage.

Pre-Procedure Planning and Tool Requirements

Before attempting to bleed a power steering system, it is vital to understand the mechanics of aeration. When air enters the high-pressure hydraulic circuit, it causes cavitation—the rapid formation and collapse of vapor bubbles. This process generates the characteristic high-pitched "whining" or "moaning" sound and can lead to internal pitting of the pump vanes. Preparation focuses on ensuring the system is sealed and that the front suspension is unloaded to allow for unrestricted movement of the steering linkage.

Essential Equipment and Materials

• OEM-Specified Fluid: Refer to your owner’s manual for the exact specification (e.g., ATF Dexron VI, Pentosin CHF 11S, or vehicle-specific Power Steering Fluid). Using the wrong fluid can cause seal swelling or total system failure.
• Floor Jack and Jack Stands: Necessary to lift the front wheels off the ground to prevent unnecessary stress on the steering components during manual cycling.
• Fluid Syringe or Turkey Baster: For removing old, aerated, or contaminated fluid from the reservoir.
• Lint-Free Microfiber Cloths: To maintain absolute cleanliness; even a small piece of lint can clog a control valve.
• Handheld Vacuum Pump with Reservoir Adapter: Optional, but highly recommended for modern vehicles with complex internal baffling that traps air.

Duration and Environment Benchmarks

• Estimated Duration: 45 to 90 minutes depending on the severity of the air intrusion.
• Budget: $20–$50 for fluid and basic supplies.
• Operational Setting: A flat, level surface with adequate lighting and ventilation.

Comprehensive Step-by-Step Power Steering Bleeding Workflow

The following procedure covers both the manual displacement method and the vacuum-assisted method. For best results, always perform the "engine-off" steps first to prevent the pump from whipping large air pockets into a fine froth, which can take hours to settle.

Step 1: Initial System Inspection and Fluid Leveling

Begin by cleaning the exterior of the power steering reservoir and the cap. Hydraulic systems are extremely sensitive to particulates. Inspect the suction hose (the larger hose leading from the reservoir to the pump) for cracks or "sweating."

1. Remove the reservoir cap and check the fluid level.
2. If the fluid is dark, smells burnt, or contains metallic flakes, a full system flush is required rather than a simple bleed.
3. Fill the reservoir to the "Max" or "Full Cold" line. Do not overfill, as the fluid needs room to expand as it heats up and to allow air bubbles to escape.

Warning: Never run the power steering pump without fluid. Running the pump "dry" for even 30 seconds can cause permanent scoring of the internal housing and vanes.

Step 2: Unloading the Steering Rack

To move the steering rack without the assistance of the engine-driven pump, you must reduce the friction between the tires and the ground.

1. Engage the parking brake and chock the rear wheels.
2. Position the floor jack under the manufacturer-approved front jacking point.
3. Lift the vehicle until both front wheels are completely clear of the ground.
4. Secure the vehicle on jack stands. Ensure the vehicle is stable before proceeding.

Step 3: Manual Air Displacement (Engine Off)

This is the most critical stage for removing large air pockets. By turning the steering wheel with the engine off, you use the rack's piston to physically push fluid and air through the return line and back into the reservoir.

1. With the engine off and the reservoir cap removed (or loosely resting on top), sit in the driver's seat.
2. Slowly rotate the steering wheel from one side to the other. Go from full left lock to full right lock.
3. Perform approximately 20 to 30 full cycles.
4. Pro-Tip: Do not slam the steering wheel against the locks. Reach the end of the travel and hold it gently for one second before reversing direction.
5. Periodically exit the vehicle and check the fluid level. As air is expelled, the fluid level will drop. Replenish as needed to keep the level at the "Full" mark.

Step 4: Vacuum Bleeding (Advanced Professional Method)

Many modern vehicles have reservoirs with internal baffles that prevent air from escaping naturally. A vacuum pump can be used to pull air out of the fluid more efficiently.

1. Insert the vacuum pump adapter into the neck of the reservoir, ensuring a tight seal.
2. Apply 15 to 20 inches of mercury (inHg) of vacuum.
3. Wait for 5 minutes. Watch the vacuum gauge; if the vacuum drops, you have a leak in the system that is allowing air to enter.
4. While maintaining the vacuum, rotate the steering wheel lock-to-lock several times.
5. Release the vacuum, remove the adapter, and check the fluid level.

Step 5: Engine-On Final Purge

Once the manual cycles no longer produce bubbles in the reservoir, it is time to test the system under pressure.

1. Check the fluid level one last time and ensure it is at the "Full Cold" mark.
2. Start the engine and let it idle.
3. Listen for any whining or groaning. If the pump is loud, immediately shut off the engine and let the fluid sit for 15 minutes; this allows the "foam" to settle.
4. If the pump is quiet, slowly turn the steering wheel lock-to-lock while the engine is idling. Perform 10 cycles.
5. Lower the vehicle back to the ground and test the steering feel. It should be smooth, consistent, and silent.

Pro-Tip: If the steering feels "notchy" or "lumpy," there is still air trapped in the steering gear (rack). Repeat the engine-off manual cycles (Step 3).

Power Steering Fluid Specifications and Material Compatibility

Choosing the correct fluid is non-negotiable. Modern steering systems use various chemical bases, and mixing them can lead to seal degradation or catastrophic pump failure.

Common System Failures and Post-Bleeding Fixes

If you have performed the bleeding process and air continues to enter the system or the noise persists, you likely have a "suction-side" leak. This is where air is drawn into the system under vacuum, even if fluid is not leaking out under pressure.

• Scenario: Persistent Whining and Foaming Fluid

  
  
  
  • Root Cause: A hardened or cracked O-ring on the pump inlet fitting. On many vehicles, the plastic nipple that the suction hose attaches to is sealed to the pump body with a single rubber O-ring. As this ages, it allows air to be sucked in.
  • Actionable Fix: Replace the inlet O-ring (usually a $2 part). Clean the fitting thoroughly before re-installation to ensure a perfect seal.

• Scenario: Fluid Overflows from Reservoir After Shut-Down

  
  
  
  • Root Cause: Massive air pocket in the steering rack or a failing internal seal in the steering gear. When the engine stops, the air pocket expands and pushes the fluid back up the return line.
  • Actionable Fix: Perform the "Engine Off" manual bleeding procedure for a minimum of 40 cycles to ensure the air is moved out of the rack's cylinder.

• Scenario: Steering is "Heavy" or "Stiff" in One Direction

  
  
  
  • Root Cause: Internal bypass in the steering rack's rotary valve or a blown piston seal. This is a mechanical failure, not an air issue.
  • Actionable Fix: The steering rack assembly must be replaced or professionally rebuilt. Bleeding will not resolve internal mechanical bypasses.

• Scenario: High-Pitched Squeal at Full Lock

  
  
  
  • Root Cause: Slipping serpentine belt or a failing belt tensioner. The power steering pump requires maximum torque at full lock, which can cause an old belt to slip.
  • Actionable Fix: Inspect the belt for glazing or cracks. Check the automatic tensioner for proper spring pressure and replace components as needed.

Frequently Asked Questions

Why is my power steering making a whining noise after a fluid change?

A whining noise after a fluid change almost always indicates that air is trapped in the pump's vanes. This creates cavitation, where the fluid cannot maintain a solid column of pressure. Perform a manual lock-to-lock bleed with the engine off to allow the air bubbles to rise into the reservoir without being homogenized into the fluid by the pump.

Can I drive with air in the power steering lines?

Driving with air in the lines is not recommended as it reduces steering assistance, leading to inconsistent control and increased driver fatigue. More importantly, the lack of constant lubrication and the heat generated by cavitation will rapidly destroy the power steering pump's internal bearings and vanes, leading to an expensive repair.

How long does it take for air to bleed out naturally?

In a perfectly functioning system, small micro-bubbles may take 24 hours to settle out of the fluid. However, large air pockets will not "work themselves out" through driving and require a manual bleeding procedure. If the fluid remains foamy after several hours of sitting, there is a mechanical leak on the suction side of the system.

Do I need a vacuum pump to bleed power steering?

While not strictly necessary for most older vehicles, a vacuum pump is highly effective for modern vehicles with low-mounted steering racks or complex reservoirs. It speeds up the process significantly by lowering the boiling point of the air bubbles, causing them to expand and rise to the surface more quickly.

Should I bleed the power steering with the cap on or off?

The bleed process should be performed with the cap off or loosely fitted. This allows the displaced air to vent into the atmosphere. If the cap is tight, the air has nowhere to go, and the pressure build-up can prevent the air from escaping the hydraulic lines.

Maintain Your Steering Integrity

To ensure long-term reliability and peak hydraulic performance, check your fluid levels monthly and address any unusual noises immediately. For further assistance with complex hydraulic diagnostics or professional-grade steering components, consult your vehicle’s factory service manual or visit a certified automotive technician.