Does power steering fluid circulate through the reservoir?

Yes—on hydraulic and electro-hydraulic power steering systems, the fluid continuously circulates through the reservoir on the low‑pressure return side before being drawn back into the pump. The reservoir is part of the loop that supplies the pump and collects return fluid for cooling, de‑aeration, and filtration. The main exception is electric power steering (EPS), which has no fluid or reservoir.

How the power steering circuit moves fluid

In a conventional hydraulic system, the reservoir feeds the pump, pressurized fluid assists steering at the gear/rack, and the fluid returns to the reservoir. This circulation occurs whenever the pump is running (engine on for belt-driven pumps, or when the electric motor runs in electro-hydraulic units).

Below is a simplified flow path in most systems:

1. Reservoir supplies fluid to the pump inlet (low pressure).
2. Pump pressurizes fluid and sends it to the steering gear/rack.
3. Steering gear uses fluid for assist; fluid exits via the return line.
4. Return line discharges into the reservoir, where air separates and fluid cools.
5. Reservoir feeds the pump again, completing the loop.

This loop ensures continuous circulation through the reservoir, allowing the system to maintain correct fluid level, temperature, and cleanliness during operation.

What the reservoir actually does

The reservoir is more than a storage cup; it conditions fluid before it re-enters the pump. Most reservoirs are baffled and include a screen or filter to improve reliability and steering feel.

• De‑aeration: Baffles and volume let entrained air rise out of the fluid, preventing foam and pump cavitation.
• Cooling: Dwell time in the reservoir helps shed heat from the fluid.
• Filtration/Screening: Internal filter or mesh captures particulates before they reach the pump.
• Head supply: Ensures a steady, gravity-fed column of fluid to the pump inlet.
• Level management: Provides an expansion space and an easy way to monitor and top off fluid.

These functions depend on consistent return flow into the reservoir and a clear, unrestricted feed back to the pump.

System variations and exceptions

Not all steering systems handle fluid the same way, but hydraulic designs still route through a reservoir on the return side.

• Remote reservoir: A separate tank connects via hoses; fluid still returns to and passes through it.
• Integrated reservoir pump: The reservoir is built into the pump housing; flow still passes through this chamber.
• Hydroboost brake systems: Share the power steering circuit; return flow still goes through the reservoir (often with multiple return ports).
• Electric Power Steering (EPS): Purely electric assist—no fluid, pump, or reservoir, so no circulation.

Regardless of layout, any hydraulic or electro-hydraulic system requires reservoir circulation for proper operation, while EPS systems are fluidless by design.

How to tell if circulation is healthy

Poor circulation shows up as noise, heavy steering, or contaminated fluid. Observing the reservoir with the cap off (engine running) can reveal issues.

• Excess foaming or bubbles: Indicates air ingestion or return turbulence; look for low fluid, loose clamps, or cracked hoses.
• Whining pump: Often due to aeration or restricted reservoir screen/return.
• Dark, burnt smell: Overheated fluid from restricted flow or failing pump.
• Jerky assist or hard steering: Possible clogged filter, kinked return, or low level.
• Fluid “churn” without smooth return: Missing/broken baffle in the reservoir or wrong fluid type.

Addressing these symptoms early protects the pump and steering gear from accelerated wear and failure.

Maintenance tips and notes

Routine checks keep the reservoir doing its job and ensure steady circulation under all conditions.

• Use the fluid specified by the vehicle maker; some require dedicated PS fluid, others allow specific ATF.
• Inspect and replace the reservoir if its internal filter is non-serviceable and suspected clogged.
• Bleed properly after service: wheels off the ground, cycle lock-to-lock with engine off, then repeat with engine on.
• Do not overfill; fluid expands when hot. Check level per manual (often warm engine, after cycling the wheel).
• For flushing, route the return line to a catch container, keep the reservoir topped, and run fresh fluid until it clears.

Following the factory procedure and maintaining the reservoir and hoses ensures the pump receives a steady, bubble-free supply of fluid.

Summary

In hydraulic and electro-hydraulic power steering systems, fluid does circulate through the reservoir as part of the normal return-and-supply loop, enabling de‑aeration, cooling, filtration, and reliable pump feed. Only electric power steering lacks circulation because it has no fluid or reservoir.

How to know if a power steering pump has air in it?

Symptoms of air in a power steering system include a whining or groaning noise, a stiff or hard-to-turn steering wheel, erratic or inconsistent power assist, and a foamy, bubbly appearance in the power steering fluid. You might also see fluid leaks, which cause low fluid levels that allow air to enter the system. If ignored, air in the system can lead to premature failure of the power steering pump and other components.
 
Common Symptoms

• Noises: A whining or groaning sound, especially when turning the steering wheel, is a primary indicator of air in the system. 
• Difficulty Steering: Steering can feel stiff, difficult, or more laborious than usual, particularly at low speeds or when making tight turns. 
• Erratic Steering: The power assist might feel inconsistent, making the steering feel unpredictable or spongy. 
• Foamy Fluid: Check the power steering fluid reservoir for a frothy, foamy, or aerated appearance, which signifies air trapped in the fluid. 
• Fluid Leaks: Low power steering fluid levels often lead to air entering the system. Look for fluid spots under your car or a need to constantly refill the reservoir. 

Why It Matters

• Component Damage: Air in the system interferes with the normal circulation of power steering fluid, which can cause the pump and steering rack to overheat. 
• Premature Failure: This overheating and lack of proper lubrication can lead to premature failure of these components. 
• Increased Effort: The lack of power assist from the air can make the steering wheel feel heavy and difficult to turn, creating a safety hazard. 

What to Do

• Check Fluid Levels: Ensure the power steering fluid is at the proper level. 
• Address Leaks: If you notice a low fluid level or fluid spots, look for and repair any leaks in the system. 
• Bleed the System: The system may need to be bled to remove the trapped air. This can often be done by turning the steering wheel lock-to-lock with the engine on and the reservoir cap off, which allows the air to escape. 

Where does power steering fluid flow through?

A high-pressure hose carries fluid from the power-steering pump to the steering rack. A low-pressure hose returns the fluid back to the reservoir. The cycle repeats as the engine is running.

Does power steering fluid flow through the rack and pinion?

Yes, power steering fluid flows through the rack and pinion in a hydraulic power steering system, where it is used to assist the driver in turning the wheels. The power steering pump sends high-pressure fluid to a piston within the rack and pinion assembly. This pressurized fluid acts on the piston to provide the force needed to move the steering rack, ultimately turning the wheels. 
How it works:

1. Pumping fluid: When the engine is running, the power steering pump circulates power steering fluid from the reservoir. 
2. Directing flow: As you turn the steering wheel, a rotary valve directs the high-pressure fluid into the rack and pinion assembly. 
3. Assisting the steering: The fluid flows to one side of the hydraulic piston inside the rack, exerting force on it. This force pushes the steering rack, which converts the steering wheel’s rotational motion into linear motion to steer the wheels. 
4. Returning fluid: Simultaneously, fluid from the other side of the piston is returned to the reservoir through a low-pressure line, completing the cycle. 
5. Neutral position: When the steering wheel is centered, the fluid flow is balanced, and there’s no significant pressure difference across the piston, allowing the fluid to simply circulate back to the reservoir. 

Why is power steering fluid not circulating?

If your power steering fluid isn’t circulating, you should first check the fluid level for leaks and air. If the fluid is full and free of air, the issue could be a broken or loose drive belt, a blocked hose or reservoir screen, or internal damage to the power steering pump or rack. A professional diagnosis is recommended if you can’t identify the problem yourself.
 
This video explains how to check the fluid level and look for leaks in the power steering system: 59s1A Auto: Repair Tips & Secrets Only Mechanics KnowYouTube · May 6, 2016
Troubleshooting Steps

1. Check for Leaks & Fluid Level: 
   • Inspect the power steering reservoir for a low fluid level. 
   • Look for any signs of fluid leaks around the pump, lines, or steering rack. 
   • If there’s no fluid, you may have a significant leak, and the pump might have been working without enough fluid, causing damage. 
2. Check the Reservoir for Air: 
   • Look for air bubbles in the power steering fluid. 
   • If you see bubbles, it indicates air in the system. Air pockets prevent proper fluid circulation. 
3. Bleed the System: 
   • With the engine off, turn the steering wheel all the way to the left and then all the way to the right. 
   • Check the fluid level again and add fluid as needed, repeating until the fluid is no longer foamy or bubbly. 
4. Inspect the Drive Belt: 
   • Check the belt that drives the power steering pump for tightness and condition. 
   • A loose or worn belt can slip on the pulley, preventing the pump from operating correctly. 
5. Check for Blockages: 
   • Look for a clogged screen at the bottom of the fluid reservoir. 
   • Inspect the power steering hoses for any internal blockages or kinks. 
6. Consider Internal System Damage: 
   • If the fluid is full, clear, and the belt is in good condition, internal issues might be the cause. 
   • Possible internal problems include a damaged power steering pump or a failing power steering rack. 

You can watch this video to learn how to diagnose internal power steering system issues, including pump and rack problems: 57s1A Auto: Repair Tips & Secrets Only Mechanics KnowYouTube · Oct 7, 2023
When to See a Mechanic 

• If you’ve performed these checks and the steering still feels hard or the fluid doesn’t circulate, it’s best to have the vehicle inspected by a professional. They can properly diagnose and repair internal component failures or complex leaks.