Hydraulic power steering: how it works and how to identify problems

Hydraulic power steering is one of the most important systems in a vehicle, as it facilitates handling and improves the driving experience. This system uses hydraulic technology to reduce the effort required when turning the steering wheel, allowing for smoother and more precise maneuvers especially at low speeds or when parking.

However, like any mechanical component, it may have problems over time and stop working correctly. In this article, we will explain how hydraulic power steering works and help you identify the most common problems so you can keep your vehicle in tip-top condition.

How does hydraulic power steering work?

Hydraulic power steering systems use the pressure generated by a special fluid to assist the driver in turning the steering wheel. Below, we break down its main components and their operation:

• Hydraulic pump. It is usually driven by a belt connected to the engine and provides the pressure needed to move the hydraulic fluid.
• Hydraulic fluid. It is a special liquid designed to transmit the force from the pump to the steering mechanism. In addition, it lubricates and protects the internal parts of the system against wear.
• Control valve (or rotary valve). It detects when the driver turns the steering wheel and directs the fluid to the corresponding side of the hydraulic cylinder.
• Hydraulic cylinder. This component converts the pressure of the fluid into mechanical movement, directly assisting the rotation of the wheels.
• Hoses and lines. They transport the hydraulic fluid between the pump, the control valve and the cylinder.

When you turn the steering wheel, the control valve redirects the pressurized fluid to the hydraulic cylinder, which applies additional force to the steering mechanism. This significantly reduces the effort you need to make when maneuvering the vehicle, making driving more comfortable and safer.

Hydraulic, electro-hydraulic, and electric (EPS) power steering: key differences

For years, hydraulic power steering was the most common system that made it easier to move the steering wheel. However, today it coexists with other more efficient and more compact systems, where the main difference is in how the steering assistance is generated:

• Hydraulic steering uses a pump and hydraulic steering fluid to generate the pressure needed to assist in turning the wheel. It is an effective and robust system, but it depends on the state of the fluid, the hoses, and the pump itself to work properly. Therefore, when there's a leak, air in the circuit, or a low level of fluid, some of the most common fault symptoms appear, such as difficulty steering wheel, vibrations, or noise when turning.
• Electro-hydraulic steering maintains that hydraulic principle, but replaces the motor-driven pump with an electric pump. In practice, it still needs fluid and retains a good part of the hydraulic components, but it improves efficiency because assistance is generated only when it is needed. It's an intermediate solution between conventional hydraulic steering and electric steering.
• Electric power steering or EPS dispenses with the hydraulic circuit. Instead of a pump, hoses, and fluid, it employs an electric motor and sensors to assist the movement of the steering wheel. This reduces maintenance, eliminates the risk of fluid leakage, and improves the vehicle's overall energy consumption. It also facilitates integration with driving assistants and automatic parking systems.

More and more cars are leaving hydraulic power steering behind

The evolution of the automobile has led more and more manufacturers to opt for electric steering. The main reason is efficiency. By not relying on a hydraulic pump or a fluid circuit, the EPS reduces mechanical losses and simplifies the assembly.

Electronics also play a role. Current driver assistance systems require steering capable of interacting with sensors, cameras, and switchboards. Electric steering fits better into that ecosystem and allows for features like lane maintenance or assisted parking more easily.(H2) Symptoms of a problem with the hydraulic power steering system

Although the hydraulic power steering system is designed to be durable and for continued use, lack of maintenance or natural wear and tear can result in failure. Identifying these issues early is crucial to prevent further damage. Let's take a look at the most common symptoms and their possible causes.

Hard or irregularly resistant steering wheel

One of the most common problems is that the steering wheel requires more effort than usual to turn. This is usually due to low pressure in the hydraulic system, caused by insufficient fluid levels, a faulty pump, or clogged hoses. If you notice this symptom, the first thing you should do is check the hydraulic fluid level in the reservoir. If it is low, fill it with the type of fluid recommended by the manufacturer. However, if the problem persists, it may be necessary to inspect the pump or hoses for possible obstructions or faults.

Noises when turning the steering wheel: what kind of sound indicates what problem

If you hear a squeak or buzz when you turn the steering wheel, something is probably not working properly. These noises often indicate hydraulic pump problems, air trapped in the system, or a worn or loose belt. A simple solution may be to adjust or replace the belt, but if the noise continues, you may need to purge the system to remove accumulated air or even replace the pump if it is damaged.

Puddles of fluid under the car

Leakage is another common problem in hydraulic systems. Over time, hoses, gaskets, or seals can deteriorate, causing fluid leakage. If you detect oil stains under the vehicle or wet residue near the steering system, it is important to act quickly. Leaks not only decrease the efficiency of the system but can also cause serious damage if not repaired in time.

Vibrations in the steering wheel

Feeling vibrations when turning the steering wheel can be a sign of various problems, from a faulty control valve to poorly balanced tires. If these vibrations occur only when turning, it is likely that the problem is related to the hydraulic system. In this case, it is advisable to go to a specialized workshop for a complete check-up.

The steering wheel does not return to the central position

When you are driving and the steering wheel does not automatically return to its central position after turning, it could be a control valve failure or incorrect wheel alignment. This problem directly affects the stability of the vehicle and should be corrected as soon as possible.

What oil or liquid does the hydraulic power steering need?

One of the most common questions is about what kind of oil is used in hydraulic power steering. The short answer is that there is no single product that is valid for all cars. Each manufacturer defines a specific specification, and that is the reference that must always be respected.

In addition to lubricating, the hydraulic power steering fluid also transmits system pressure, helps dissipate temperature, protects against wear, and helps keep internal components clean.  Therefore, an incorrect product can affect the feel of the steering, cause noise, damage seals, or alter the operation of the pump. Therefore, it is always advisable to review the vehicle's manual and check the exact specification required by the manufacturer.

Types of liquid: mineral, synthetic and semi-synthetic — which one to use according to the manufacturer

Generally, the hydraulic power steering fluids may be mineral, synthetic, or semi-synthetic. The difference between them is in their base and in the additive package, which influences aspects such as thermal stability, viscosity, protection against wear, or compatibility with seals and circuit materials. However, the manufacturer's recommendation must always be taken into account above any other consideration.

How to prevent problems with the hydraulic steering system

Hydraulic power steering is an essential system to ensure comfortable, safe, and efficient driving. Understanding how it works and keeping an eye out for symptoms of potential problems can help you prevent breakdowns and keep your vehicle in optimal condition. If you detect any failures, do not ignore the signs, and act quickly to avoid further damage.

At Repsol Lubricants, we have high quality products designed to protect and optimize the performance of your vehicle's hydraulic systems. Use the search engine on our website to find the hydraulic fluid you need by simply searching for the model of your vehicle or its license plate.

Frequently asked questions about hydraulic steering

What kinds of hydraulic power steering fluids exist?

The two most common types are mineral and synthetic hydraulic power steering fluid. In some cases, semi-synthetic formulations or specific fluids that share a base with other hydraulic systems of the vehicle are also used. The difference between them lies not only in their composition, but also in their compatibility with pumps, seals, gaskets, and internal tolerances. The important thing is to check the specification indicated by the manufacturer in the manual.

Why does hydraulic power steering make noise when turning the steering wheel?

When the hydraulic steering makes noise when turning the steering wheel, the most frequent thing is that there is a low level of liquid, air in the circuit, or a worn-out pump. That noise can be perceived as a buzzing, moaning, or a harsher sound when moving the steering wheel, especially when steering at low speeds.

It can also be due to a deteriorated liquid, a bad belt, or a leak that is causing the system to lose pressure. In any case, it is advisable to check the circuit as soon as possible. Ignoring it can make the breakdown worse and increase wear and tear.

How often do I need to change the hydraulic power steering fluid?

There is no universal range for the change of hydraulic steering fluid. It depends on the manufacturer, the type of system, and the use of the vehicle. In some models, the manual sets a specific deadline; in others, it's a good idea to check it periodically and replace it when it loses properties. One practical option is to check its level and condition at each maintenance.

This isn't recommended. A faulty hydraulic power steering can harden the steering wheel significantly and compromise the control of the vehicle. Furthermore, if the problem comes from a leak or a damaged pump, continuing to circulate may aggravate the breakdown. If you notice that the steering wheel has become rigid, that it makes noise when turning, or that the system is leaking fluid, you should stop driving when possible and take your car to the shop.

What's the difference between hydraulic and electro-hydraulic power steering?

The main difference is in how the power steering pump works. In conventional hydraulic steering, the pump is usually driven by the vehicle's own engine. In electro-hydraulic steering, the pump is operated thanks to an independent electric motor. Both need hydraulic steering fluid and share much of the logic of the system, but electro-hydraulics improves efficiency because it does not consume energy permanently.

What happens if different types of hydraulic steering fluid are mixed?

Mixing different types of hydraulic steering fluid can generate chemical incompatibilities and affect system operation. Depending on the formulation, the mixture can alter the viscosity, reduce the lubricating capacity, affect the seals, or favor the appearance of foam and noises.