What Happens If Air Gets in Your Power Steering Pump

Air in a power steering pump aerates the fluid, causing whining or groaning noises, foamy fluid, jerky or heavy steering, and reduced assist; left unresolved, it can overheat the fluid and damage the pump and steering rack. This article explains why air is harmful, how to spot it, what causes it, and the safest ways to fix and prevent it.

Why Air in a Hydraulic Power Steering System Is a Problem

Hydraulic power steering depends on incompressible fluid to transmit force. When air enters the system, the mixture compresses under pressure and creates tiny vapor bubbles—an effect called cavitation. Cavitation disrupts pressure, reduces steering assist, generates heat, and can pit metal surfaces inside the pump and steering gear. The result is noisy operation, inconsistent steering feel, and accelerated wear.

Common Signs and Immediate Effects

These are the symptoms most drivers notice when air has entered the pump or lines, often after a fluid leak or recent steering service.

• Whining, groaning, or moaning that gets louder as you turn the wheel or raise engine RPM.
• Foamy, milky, or bubbly fluid visible in the reservoir; fluid may overflow or spit from the cap.
• Intermittent, heavy, or jerky steering assist—especially at low speeds or when parking.
• Vibration or chattering felt in the steering wheel during turns.
• Hot, burnt smell from the fluid after driving; in severe cases, fluid darkening.
• If your vehicle uses a hydroboost brake system (brake assist powered by the steering pump), a firmer brake pedal may accompany steering issues.

If these signs appear, continuing to drive can worsen damage. Address the root cause—usually a leak or improper bleeding—and then purge the air.

Long-Term Risks and Damage

Persistent aeration does more than make noise; it harms components and can lead to failure.

• Cavitation pitting of pump vanes and rotor, shortening pump life and increasing noise.
• Overheating and oxidation of fluid, which degrades lubricity and hardens seals.
• Wear or scoring inside the steering rack’s spool valve and rack seals, risking leaks and stiff steering.
• Increased load on the drive belt and pulley, which can cause belt glazing or squeal.
• In extreme cases, loss of power assist—especially hazardous at low speeds.

Timely correction—sealing air leaks and bleeding—prevents these costly outcomes.

Likely Causes of Air Intrusion

Air most often enters on the low-pressure (return/suction) side of the system, where even tiny gaps can draw air without showing visible fluid leakage.

• Low fluid level from a leak at hoses, cooler, pump, or steering rack.
• Loose clamps, cracked or hardened return hoses, or porous hose material.
• Worn or flattened O-ring at the pump inlet fitting (common on some GM, Honda/Acura, and other makes).
• Cracked reservoir, missing/failed cap seal, or reservoir filter screen restrictions that promote aeration.
• Recent service (pump, rack, lines) without proper bleed procedure.
• Incorrect fluid type that foams more easily than the specified power steering fluid or ATF.

Confirming and fixing the source of air intrusion before bleeding saves time and prevents repeat issues.

How to Fix: Bleeding the Power Steering System

Basic DIY Bleed (Most Hydraulic Systems)

This method works for many vehicles after leaks are repaired. Always use the fluid specified in your owner’s manual or service information.

1. Safely raise the front wheels off the ground and secure the vehicle.
2. Fill the reservoir to the “COLD” mark with the correct fluid.
3. With the engine OFF, slowly turn the steering wheel from lock to lock 20–30 times. Do not force it hard against the stops.
4. Recheck the reservoir; top up as bubbles purge and the level drops.
5. Start the engine and let it idle. Slowly turn lock to lock 5–10 times, avoiding holding at full lock for more than 2–3 seconds.
6. Watch the reservoir for bubbles or foam; shut off and let it sit a few minutes. Repeat cycling until the fluid runs clear and bubble-free.
7. Lower the vehicle and take a short, gentle drive with wide, slow turns. Avoid parking-lot maneuvers that force full lock.
8. Recheck fluid level and inspect for leaks. Top off as needed.

If the fluid continues to foam or the pump whines after multiple cycles, a vacuum bleed or further leak diagnosis is recommended.

When Vacuum Bleeding Is Better

Some systems trap air stubbornly. A hand vacuum pump and reservoir adapter can de-aerate fluid quickly and thoroughly.

1. Attach a reservoir adapter and connect a hand vacuum pump.
2. Apply 20–25 inHg of vacuum for 5–10 minutes. With the engine OFF, slowly cycle the steering wheel to move air pockets.
3. Release vacuum, top up fluid, and repeat until no bubbles appear under vacuum.
4. Start the engine, briefly cycle the wheel, and verify quiet operation. Top off to the correct mark.

Vacuum bleeding is especially useful after replacing a pump or rack, or on systems with long lines and coolers that trap air.

After the Bleed: Verification

Confirming the repair prevents repeat visits and component damage.

• Reservoir fluid is clear, not foamy, with no visible bubbles.
• Pump operates quietly at idle and during slow turns.
• Steering assist is smooth and consistent in both directions.
• No fresh fluid around hose connections, pump, or rack boots.
• Fluid level remains stable after an overnight cold soak.

Any persistent noise or level changes suggest a remaining leak, restriction, or component fault.

Prevention Tips

Routine checks and correct service practices reduce the chance of aeration recurring.

• Check the reservoir monthly and top up with the specified fluid only.
• Replace aging return hoses and clamps proactively; inexpensive parts prevent air leaks.
• Renew the pump inlet O-ring during pump or hose service; lubricate seals with fresh fluid on assembly.
• Avoid holding the wheel at full lock for more than a couple of seconds to limit heat and pressure spikes.
• Flush or exchange fluid if it turns dark, smells burnt, or after major component replacement (follow manufacturer guidance).
• Inspect the serpentine belt and tensioner; slip can mimic pump whine and reduce assist.

Good maintenance practices protect the pump and rack, extending system life and keeping steering feel consistent.

When to Seek Professional Help

Some conditions indicate deeper faults or safety-critical issues that warrant a qualified technician.

• Whine or foam persists after proper bleeding and leak repair.
• Rapid fluid loss or visible drips from the rack boots or pump shaft.
• Metallic glitter in fluid, indicating internal wear or failure.
• Steering is stiff in one direction only, pointing to a rack or spool valve issue.
• Vehicles with electric power steering (no hydraulic pump) require different diagnostics; noises may come from the EPAS motor or column.
• Hydroboost brake complaints along with steering issues—brake assist is a safety system.

Prompt professional diagnosis prevents cascading failures and higher repair costs.

Costs and Time Estimates

Actual costs vary by vehicle, labor rates, and parts quality, but these ballpark figures can help you plan.

• Bleed procedure: 0.5–1.0 hour; $0–$150 (DIY vs. shop).
• Inlet O-ring or return hose/clamps: $5–$30 parts; 0.5–1.0 hour labor.
• Pump replacement: $200–$600 parts; 1–3 hours labor.
• Rack and pinion replacement: $400–$1,200 parts; 3–6 hours labor.
• Fluid: $8–$25 per quart; 1–3 quarts typical for service.
• Vacuum bleed tool/adapter (if DIY): $30–$80.

Addressing air and small leaks early is usually inexpensive; delayed repairs risk pump or rack replacement costs.

Bottom Line

Air in a power steering pump leads to noisy, inconsistent steering and can quickly damage the pump and rack through cavitation and overheating. Fix the source of the air, use the correct fluid, bleed the system thoroughly (vacuum bleed if needed), and verify quiet, bubble-free operation. Early attention keeps steering safe, quiet, and affordable to maintain.

What does air in a power steering system sound like?

And may also notice it may be difficult to steer. If you find yourself constantly topping off the power steering reservoir with fresh power steering fluid you definitely have a leak somewhere.

How do you fix aerated power steering fluid?

Foaming Power Steering Fluid Solutions
If air’s getting in through worn seals, o-rings, or hoses, flush the system and replace those parts before refilling the system with new fluid. You can also try to bleed the power steering system of air.

What happens if air gets in power steering?

Air in the power steering system causes symptoms like a harder, jerky steering wheel, a growling or whining noise from the pump, and visible bubbles in the fluid reservoir. If left unaddressed, air in the hydraulic system can cause the power steering pump to fail prematurely and lead to reduced steering performance. To fix it, you must bleed the air out of the system by adding the correct power steering fluid, turning the steering wheel lock-to-lock with the engine running, and repeating until the fluid is air-free.
 
Symptoms of Air in the Power Steering System 

• Noise: You may hear a persistent growling, whining, or grunting noise, especially when turning the steering wheel.
• Hard Steering: Steering feels stiff, difficult, or jerky.
• Bubbles in the Reservoir: The power steering fluid in the reservoir may appear foamy or have visible bubbles, which indicates air in the fluid.
• Leaking Fluid: Air intrusion often points to a leak in the system, which could be at a hose, fitting, the pump, or the steering rack and pinion.

Why Air is a Problem

• Reduced Performance: The hydraulic system relies on fluid for pressure, and air disrupts this, making steering effortless. 
• Pump Damage: The power steering pump is designed to work with fluid. When air is present, the pump can overheat and fail, which can also cause the accessory belt to snap. 
• System Failure: In severe cases, a failing pump or a leak can lead to a complete loss of power steering. 

How to Bleed Air from the System

1. Check Fluid Level: Ensure the power steering fluid is filled to the recommended level using the correct type of fluid. 
2. Start the Engine: With the engine running, turn the steering wheel slowly from one full lock to the other. 
3. Monitor Fluid Level: After each turn, shut off the engine and check the fluid level. Add fluid as needed. 
4. Repeat: Continue turning the steering wheel from lock to lock and adding fluid until the growling noises stop and the fluid no longer shows bubbles. 

How to get trapped air out of a power steering pump?

To get air out of a power steering pump, slowly turn the steering wheel from full lock to full lock with the engine off, then start the engine and repeat the process while monitoring the fluid level, adding more fluid as needed. Ensure the front wheels are lifted off the ground to prevent unnecessary wear and make the steering easier. For stubborn cases, a vacuum pump can be used to draw air from the system. 
Method 1: Turning the Steering Wheel

1. Prepare the vehicle: Park on level ground and lift the front of the vehicle using a jack to keep the wheels off the ground. 
2. Check the fluid: Open the hood, locate the power steering fluid reservoir, remove the cap, and check the fluid level. Top it off to the “Full Cold” line with the correct fluid for your vehicle. 
3. Bleed the system (engine off): With the engine off, turn the steering wheel slowly from the full left to the full right position. 
4. Repeat: Stop at the center, check the fluid level, and add more fluid to keep new air from entering the hoses. Repeat this process 12 to 15 times. 
5. Start the engine: Start the engine. 
6. Bleed the system (engine running): Turn the steering wheel from full lock to full lock again, slowly. Check the fluid level and add more fluid as needed. Continue this until the fluid is no longer foamy or bubbly. 

This video shows how to bleed the power steering system by turning the steering wheel lock to lock: 1mWorld MechanicsYouTube · Mar 3, 2016
Method 2: Using a Vacuum Pump

1. Prepare for vacuum: Install a vacuum adapter into the power steering reservoir cap. You may need to drill a hole in the cap to fit a fitting for the vacuum pump. 
2. Apply vacuum: Attach a vacuum pump to the adapter. 
3. Start the engine: Start the engine and let it idle. 
4. Draw vacuum: Apply 20-25 inches of vacuum to the pump. You will hear the pump make noise as it pulls air from the system. 
5. Turn the steering wheel: While the vacuum is applied, turn the steering wheel from stop to stop about 10 times. 
6. Check fluid level: Turn off the engine and release the vacuum. Check the fluid level and add more if needed. 
7. Repeat if necessary: If the fluid is still bubbly, repeat the process, as air may still be trapped in the system. 

Tips for Success

• Use the correct fluid: Always use the power steering fluid recommended in your owner’s manual. 
• Don’t overfill: Keep the fluid level at the specified line to prevent new air from entering the system. 
• Be patient: It may take multiple cycles of turning the wheel or a combination of both methods to remove all the air.