Seastar hydraulic steering fluid

Seastar hydraulic steering fluid: SeaStar Solutions Hydraulic Fluid is formulated to optimize performance and maximize the life of the steering system.

SeaStar Solutions designs hydraulic steering systems for maximum performance, regardless of boat type or propulsion. Users and technicians alike respect his consistency and expertise across the industry.

As seal technology, composition and design have evolved, so has the chemistry of hydraulic fluid. SeaStar Hydraulic Fluid is specifically designed to maximize the performance and life of SeaStar steering systems. Corrosion and oxidation inhibitors combined with anti-wear agents keep contamination to a minimum and increase ram and seal longevity. Viscosity stabilizers and antifoam agents are added to provide consistent and predictable performance. Water emulsion additives reduce moisture content that can cause damage and compromise steering.

To ensure industry leading performance, SeaStar only approves SeaStar Power Steering Fluid for use in its steering systems.

key features

  • Designed to maximize the life of the entire steering system
  • Proprietary additives control contaminants that can negatively affect steering performance
  • Formulated not to damage components including hoses, rams and rudder pumps
  • Reduces steering effort regardless of ambient temperature
  • Only steering fluid approved for use in SeaStar Solutions steering systems

What you should know about this often overlooked marine system.


Some marine systems are so reliable that we tend to go unnoticed. I’ve had a few boats in my time, and most of them had power steering. It’s one of those reliable systems so widespread that it’s nearly universal except for ships that use a rudder, cable, or other form of mechanical steering. Good steering systems work as they should, year after year, and usually don’t stick to the routine maintenance schedule unless there is a problem.

But that might not be the best of ideas. After all, he’s on a boat, and nothing on a boat is perfect or forever. Does hydraulic fluid go bad over time? Do the accessories work loose? Are there any common failure points I should be aware of? So how often should you think about these things and what exactly are you looking for? To find some answers, we spent some time with Chad Winget, lead technician at Zimmerman Marine, a well-respected service and repair facility in Deltaville, Virginia, whose ABYC-certified technical staff knows how things should be done. When we met, he explained power steering in layman’s terms, showing what to look for and how best to ensure a trouble-free system, no matter what type of boat you’re on.


Power steering consists of three components: a pump with an integral reservoir for hydraulic oil, a ram that connects to a rudder or outboard motor, and connecting lines that transmit information from the steering pump to the steering ram. It’s very simple and when sized and installed correctly makes for a mostly carefree system. Turning the steering wheel in either direction pumps oil through the lines to the piston, which in turn pulls or pushes the tiller, outboard, or sterndrive in the desired direction.


The simplest example of hydraulic steering is found on small power boats powered by a single outboard motor or multiple engines linked by a tie rod. On a small boat, a compact hydraulic pump with an integral hydraulic fluid reservoir located in the steering wheel connects with strong nylon hoses below deck and in turn with flexible rubber hoses to a steering piston in the transom stern, which reliably rotates outboard motors. as one turns the steering wheel. Steering systems get more and more complicated on larger boats with multiple rudders, autopilots, and power steering, but the basics are pretty much the same. So is maintenance.

Winget recommends an annual inspection. Watch for seals on the ram, especially in an open boat, where it is exposed to salt, sand, fishing line, and other potential hazards. The shaft must never be wet with oil. If so, wipe it dry and check again while you cycle the steering. If a wet shaft comes out of the ram, the seals are leaking and need to be replaced. Check the shaft for pitting, a sign of corrosion that will eventually cause hydraulic fluid to leak from the cylinder.


Remove the vented cap from the hydraulic reservoir at the helm and take a sample of the hydraulic oil. Does it look black? Smells? Power steering fluid is clear, mostly odorless, and light in color. It is specially formulated with viscosity stabilizers, anti-wear and anti-foam agents, and corrosion inhibitors. It is the best oil to use in power steering systems, but any oil that meets the MIL 5606 specification can be used, and in an emergency, even 5W motor oil. While many boaters use automatic transmission fluid in their steering systems, using the manufacturer’s recommended product is the way to go.


If the power steering oil sample contains dirt or is otherwise contaminated, the entire system should be flushed and the hydraulic oil replaced. Abrasive dirt is the biggest killer in hydraulic systems. It often comes from debris during the initial installation of the steering system. Dirt or dust can enter the system when hoses are cut and fittings are installed. It is best to flush a steering system before the final hydraulic oil enters, something to keep in mind when performing a repair. Your hydraulic system should be flushed and oil replaced every five years, including fully bleeding the system to remove air bubbles. Many service yards use portable purge systems that make this a quick and foolproof job that only takes a few minutes.

What hydraulic fluid should you use?

Most hydraulic systems will work satisfactorily using a variety of fluids. These include motor oil, automatic transmission fluid, and oil specifically formulated for the hydraulic compartment. But what type of fluid is best for a particular application? While it is not possible to make a definitive recommendation that covers all types of hydraulic equipment in all applications, the following are some of the factors that should be considered when selecting (or changing) a hydraulic fluid.


Most hydraulic systems will work satisfactorily using a variety of fluids. These include motor oil, automatic transmission fluid, and oil specifically formulated for the hydraulic compartment. But what type of fluid is best for a particular application? While it is not possible to make a definitive recommendation that covers all types of hydraulic equipment in all applications, the following are some of the factors that should be considered when selecting (or changing) a hydraulic fluid.

Multigrade or Monograde

Viscosity is THE most important factor when selecting a hydraulic fluid. No matter how good the other properties of the oil are, if the viscosity grade is not correctly matched to the operating temperature range of the hydraulic system, maximum component life will not be achieved. Defining the correct fluid viscosity grade for a particular hydraulic system involves consideration of several interdependent variables. These are:

  • initial viscosity at minimum ambient temperature (lowest cold start temperature);
  • maximum expected operating temperature, which is influenced by the maximum ambient temperature; Y
  • permissible and optimal viscosity range for system components.

If the hydraulic system is required to operate in sub-zero temperatures in winter and tropical conditions in summer, multi-grade oil will likely be required to maintain viscosity within allowable limits over a wide operating temperature range. If the fluid viscosity can be kept in the optimum range, typically 25 to 36 centistokes, the overall efficiency of the hydraulic system is maximized (less input power is delivered to heat). This means that, under certain conditions, the use of a multigrade oil can reduce the energy consumption of the hydraulic system. For users of mobile hydraulic equipment, this translates into lower fuel consumption.


There are some precautions when using multigrade fluids in hydraulic systems. Viscosity index (VI) improvers used to make multigrade oils can have a negative effect on the air-separating properties of the oil. This is not ideal, particularly in mobile hydraulic systems that typically have a relatively small reservoir with a corresponding reduction in deaeration characteristics.


And if you use a multigrade that is not specifically formulated for use in hydraulic systems, such as motor oil, the high shear rates and turbulent flow conditions that often occur in hydraulic systems destroy the molecular bonds of the VI improvers over time, resulting in a loss of viscosity. For this reason, if a multigrade motor oil is used in a hydraulic system, it is recommended that the minimum allowable system viscosity values ​​be increased by 30% to compensate for the reduction of the VI improver.


However, if the hydraulic system has a narrow operating temperature range and it is possible to maintain optimal fluid viscosity with a monograde, it is wise to ‘keep it simple’ and not use a more complex multigrade oil.

Detergent or No Detergent


DIN 51524 standard; HLP-D fluids are a class of anti-wear hydraulic fluids that contain detergent and dispersant additives. These fluids are approved for use by most major manufacturers of hydraulic components. Detergent oils have the ability to emulsify water and disperse and suspend other contaminants such as varnish and sludge. This keeps the components free of deposits, but means that contaminants don’t precipitate out, they have to be filtered out. These can be desirable properties in mobile hydraulic systems which, unlike industrial systems, generally have reduced opportunity for settling and precipitation of contaminants in the reservoir, due to their relatively small volume.


The main caution with these fluids is that they have excellent water emulsifying capacity, meaning that if water is present, it will not separate from the fluid. Water accelerates oil aging, reduces lubricity and filterability, reduces seal life, and causes corrosion and cavitation. And emulsified water can turn to steam in highly charged parts of the system. These problems can be avoided by keeping the water content below the saturation point of the oil at operating temperature.


Antidesgaste o R&O


The purpose of antiwear additives is to maintain lubrication under boundary conditions. The most common anti-wear additive used in engine and hydraulic oil is dialkyl zinc dithiophosphate (ZnDTP). This is slowly changing due to environmental considerations, as zinc is a ‘heavy’ metal. The presence of ZnDTP in oil is not always considered positive, due to the fact that it can chemically break down and attack some metals and reduce filterability. The chemistry of stabilized ZnDTP has largely overcome these shortcomings, making it an essential additive to fluid used in any high-pressure, high-performance hydraulic system, such as those equipped with piston motors and pumps. A ZnDTP concentration of at least 900 PPM can be beneficial in mobile applications and is recommended by some OEMs.


You may not know how hydraulic oil is different from transmission oil. In this article we will compare them with each other. If you are new or learning more about hydraulic oil or transmission oil or just looking for a guide on the difference between the two, you came to read the right article.


Hydraulic oil and transmission oil transmit power in hydraulic equipment. It is also used in power transmission applications. They are incompressible oils used as a power transmission medium in hydraulic systems.



Hydraulic oil is a medium that transmits power in a hydraulic system. Viscosity, wear protection, oxidation stability, and resistance to foaming are typical factors that help determine the type of hydraulic oil. Hydraulic oil is typically classified by its function within a system. It can fulfill more than one of these broad functions, such as:

  • avoid corrosion
  • dissipating the heat
  • Lubrication of system pumps, valves and cylinders
  • Hydraulic power transfer

In addition to their primary function, hydraulic oils share certain properties that make them suitable for use in hydraulic systems. Here are the following:

  • Lubricity
  • chemically and physically stable
  • The temperature
  • Low foaming properties
  • Fire and flash resistance

And other physical characteristics.

transmission oil

Transmission oil or transmission fluid is a type of oil that helps lubricate the moving parts within the transmission. Automatic transmissions also use the fluid as a coolant. Transmission oil is designed for automatic and manual transmissions. The oils involved are different for each type of system.

Some automatic transmission systems use automatic transmission fluid, also known as ATF, as a hydraulic fluid and gear lubricant. ATFs can be pressurized by a pump and regulated by valves in a similar way to other hydraulic systems.

Manual transmissions use appropriate gear lubricants that can range from straight mineral oil to synthetic fluid.

If you find this post about Seastar hydraulic steering fluid helpful to you and you want to know more about car fluid knowledge, please check more on our website Auto Oil And Fluid. Thank you for your interest!



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