How to Get Trapped Air Out of a Power Steering System

You can remove trapped air from a hydraulic power steering system by safely lifting the front wheels, topping up the correct fluid, cycling the steering wheel lock-to-lock with the engine off, then repeating with the engine running while monitoring and refilling the reservoir; a hand vacuum bleeder on the reservoir speeds the process. This step-by-step approach reduces foaming, restores smooth assist, and prevents pump damage. Below, we explain why air gets in, how to bleed it correctly, and what to do if noise or bubbles persist.

Why Air Gets Trapped—and What It Sounds Like

Air infiltrates power steering systems through low fluid levels, loose hose clamps, cracked return hoses, worn pump shaft seals, or after component replacement. Typical symptoms include a high-pitched whine that rises with engine speed, jerky or notchy steering, and foamy or milky fluid in the reservoir. Because air reduces hydraulic pressure and can cavitate the pump, bleeding it promptly protects the system from premature wear.

What You’ll Need

Gathering the right tools and supplies ensures a controlled, clean bleed that won’t introduce more air or contamination.

• Correct power steering fluid (or manufacturer-specified ATF) and a clean funnel
• Floor jack and jack stands or ramps; wheel chocks
• Gloves, rags, and eye protection
• Hand vacuum pump with reservoir cap adapter (optional but effective)
• Turkey baster or fluid syringe for extracting foamy fluid (optional)
• Shop light to inspect hoses and clamps for leaks

With these items ready, you can perform a thorough bleed and inspect for the root cause that introduced air in the first place.

Step-by-Step: Manual Bleed Without Special Tools

This method uses basic tools and careful steering cycles to purge air through the reservoir where it can escape.

1. Confirm the system type. If your vehicle uses full electric power steering (EPS), there is no fluid to bleed. If it’s hydraulic or electro-hydraulic (electric pump + fluid), proceed.
2. Park on level ground, set the parking brake, chock the rear wheels, and raise the front so both tires are off the ground. Support the vehicle securely with jack stands.
3. Identify the correct fluid specified in your owner’s manual and fill the reservoir to the “COLD” mark. Do not overfill.
4. With the engine off, slowly turn the steering wheel from lock to lock 15–20 times. Pause briefly at each end; do not hold against the stop. Watch the reservoir for bubbles and a dropping level; top up as needed.
5. Let the vehicle sit 5–10 minutes to allow foam to dissipate. If the fluid is exceptionally foamy, extract the froth from the top and refill with fresh fluid.
6. Start the engine and let it idle. Slowly turn lock to lock 5–10 times. Limit time at full lock to under 5 seconds. Continue monitoring fluid level and clarity; add fluid as it purges air.
7. Shut the engine off and wait several minutes. Recheck level and foam. Repeat the running lock-to-lock cycles until bubbles stop appearing and steering feels smooth and quiet.
8. Lower the vehicle, take a short, gentle drive with wide steering sweeps, then recheck the fluid level and condition. Top up to the “HOT” mark (after reaching operating temperature), if applicable.

Done correctly, this procedure clears most trapped air and restores normal steering assist without stressing the pump or seals.

Faster Method: Vacuum Bleed at the Reservoir

Applying vacuum at the reservoir helps air expand and escape quickly, which is especially useful after replacing racks, lines, or pumps.

1. Fit a reservoir cap adapter connected to a hand vacuum pump. Ensure all hose connections are airtight.
2. Fill to the “COLD” mark with the specified fluid. Apply 20–25 inHg of vacuum and hold for 3–5 minutes. You’ll often see bubbles rising through the fluid.
3. Release vacuum slowly to avoid splashing. Refill as needed. Repeat the vacuum-and-release cycle 2–3 times until bubbling slows significantly.
4. With vacuum applied at about 15–20 inHg, start the engine and let it idle for 30–60 seconds, then shut off. Carefully release vacuum and check level. Repeat brief idle cycles while maintaining vacuum until bubbles cease.
5. Remove the adapter, set the fluid to the correct mark, and perform 3–5 slow lock-to-lock turns with the engine running as a final check.

Vacuum bleeding minimizes the number of steering cycles and reduces the risk of aeration during the first startup after major repairs.

Check for Leaks That Reintroduce Air

If noise returns or bubbles keep forming, a small suction-side leak may be drawing air into the system. A focused inspection can prevent repeated bleeding.

• Low-pressure return hose: Look for dampness, cracked rubber, or loose spring clamps; upgrade to worm-gear clamps where appropriate.
• High-pressure line: Inspect crimp fittings and banjo bolt washers for seepage.
• Pump shaft seal: Check behind the pulley and around the pump body for wetness or sling marks.
• Reservoir: Some have internal filters that clog and cause cavitation; replace if restricted or cracked.
• Rack and pinion: Torn boots or fluid inside boots can indicate internal leaks.

Addressing these points ensures air doesn’t re-enter and that your bleed results hold over time.

Important Notes on Fluid and Procedure

Manufacturers specify fluid for a reason: using the wrong type can cause noise, seal wear, or poor assist. Honda and some European brands mandate proprietary PSF, while others allow certain ATFs. Always confirm.

• Never overfill; fluid expands when hot. Aim for the correct mark for the current temperature.
• Avoid holding the steering at full lock for more than a few seconds—it can overheat fluid and stress the pump.
• If the fluid is dark, burnt-smelling, or contaminated, consider a full fluid exchange via the return line while keeping the reservoir topped to avoid ingesting fresh air.
• After major component replacement, expect to repeat the bleed after a short drive as residual microbubbles work out.

Following these guidelines helps maintain pump health, steering feel, and long-term reliability.

When to Seek Professional Help

Persistent whining, heavy steering, or rapid bubble formation after multiple bleed attempts suggests a mechanical fault. A shop can pressure-test the system, check pump output, verify rack valve function, and perform a machine-assisted vacuum bleed if needed.

Safety Reminders

Work on a cool engine, support the vehicle on stands, keep hands clear of belts and pulleys, and clean spilled fluid immediately—it’s flammable and slippery. Dispose of used fluid according to local regulations.

Summary

To purge trapped air from a hydraulic power steering system, lift the front wheels, fill with the correct fluid, cycle the steering slowly with the engine off and then running, and top up as bubbles escape; a vacuum bleeder at the reservoir accelerates the process. If air returns, inspect for suction-side leaks, deteriorated hoses, or a failing pump, and verify you’re using the manufacturer-specified fluid. These steps restore quiet, smooth steering and protect the system from damage.

How long does it take to get air bubbles out of power steering?

First make sure it’s full. Then start it up, turn the steering wheel all the way left then all the way right, two times slowly. Then shut it off. Wait 10 minutes and repeat, if it seems there still air it should disappear with normal driving.

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.

How to get air out of power steering without a vacuum pump?

You remove the lid of the fluid reservoir, top up the fluid, and turn the steering wheel from lock to lock a few times. This should remove the air from the system. The you top up the fluid again – if it needs it, and repeat the process until it doesn’t.

How to get air out of power steering?

To remove air from a new power steering pump, first fill the reservoir with the correct fluid. With the engine off, turn the steering wheel fully left and right several times to circulate fluid and release trapped air. Then start the engine and repeat steering motions slowly.