Hydraulic Fluid Selection Guide

Hydraulic fluid is a versatile, multi-function necessity for machinery everywhere. You would be hard pressed to find a machine that doesn’t require hydraulic fluid to maintain performance and reduce component wear as hydraulic systems are hard on the parts within them. As a business that operates machinery, there is also the requirement to comply with mandatory machine safety standards to stay in the legal operating zone.

Running a business with multiple machines means you need to know how to select the best hydraulic fluid for the machinery in your shop. It’s also a possibility you may need to know the best hydraulic fluid for multiple types of machinery while also staying on top of servicing schedules.

Functions of hydraulic fluid

Hydraulic fluid is what transfers energy in the hydraulic system while also providing lubrication, sealing, heat transfer, and contamination removal at the same time to prevent hydraulic component wear while ensuring optimal performance.

It provides both heating and cooling functions in the system, can be a sealant through the shear resistance and surface tension, supplies a mostly metal on metal system with full film lubrication, and removes contaminants when bled off.

Types of hydraulic fluid

Most hydraulic fluids, or oils, are refined or synthetic oil based with a few exceptions of a water based hydraulic fluid. Made up of a base oil (usually about 98% of the fluid) and additives to get the best possible performance in its intended use, hydraulic fluid is specifically formulated to certain purposes.

Base oils come in different grades, which will provide different properties in the final product and not every fluid has the same additives. Most additives are preventative in nature and used to help reduce component wear. Different additives also provide different qualities to the hydraulic fluid.

While it may require a degree to completely understand the science behind hydraulic fluid formulation what’s important to know is how to choose the right fluid to keep your machines running at their best.

Especially since choosing the wrong hydraulic fluid could lead to component wear, system failure, or regulation non-compliance. All of those scenarios lead to extra dollars being spent that didn’t have to be along with delayed work time due to lack of machinery.

So, how do you choose the best hydraulic fluid?

It would take an in-depth, incredibly long article to fully break down all of the hydraulic fluid nuances, here we have provided a brief overview of what to look for.

Know that going off the label can be misleading as there are subtle differences between manufacturer approved and the fluid meeting the requirements of the manufacturer. In a general sense following what is approved by the manufacturer will lead you to a better choice than the claim that it meets the manufacturers requirements you will see on many bottles.

Approved means it has been tested to ensure performance over just being formulated to work according to the system requirements and with hydraulic fluid, you want to know it will stand the test of both time and usage.

hydraulic fluid Stainless Steel Tube Fitting

Let’s break this down a little further.

Multi-grade or mono-grade: what type you buy will be determined by how much of an operating temperature range there is.  The wider the range; the more likely you need multi- grade to maintain the viscosity. If there is a narrow temperature window, you can save the money and go with mono-grade if the fluid viscosity can be maintained at the optimum level.

Viscosity: this is how the fluid flows through the system, obviously an important factor in hydraulic fluid to ensure optimal performance while reducing component wear. The viscosity index (VI) tells you how it will flow over a range of temperatures. The higher the fluid rates on the VI, the more it maintains a consistent level of quality over the measured temperature ranges. With the technology today, VI improving additives can also be made to be more shear resistant, meaning they can withstand more use before breaking down.

Pour point refers to the temperature needed for the oil to still pour. Hydraulic fluid with a lower pour point will be better functioning in cold weather than a fluid with a higher pour point.

Water is not your friend in the hydraulic system at all as it creates contamination while degrading performance and increasing component wear. To combat this, a detergent may be added that will emulsify or demulsify the water.

Emulsifiers suspend the water in the system while demulsifiers separate it and require reservoir draining. Along with the water, hydraulic fluids with detergent additives also remove other types of contamination that can cause problems.

However, not all machines need the added detergent to remove contaminants; it is mostly suggested for the smaller, mobile hydraulic machines and not always necessary for the larger, industrial machines that have more volume for contaminants to settle and not be put into circulation.

Anti-wear additives are important to the life of the hydraulic fluid to keep the lubrication properties as the fluid ages while also stopping wear and oxidation. The most common anti-wear addictive is ZDDP, which may also cause problems if it breaks down with water present or reacts with yellow metals. However, ZDDP free fluids are more expensive and haven’t been as extensively tested to guarantee they will provide the anti-wear protection needed.

hydraulic fluid selection: worker looking at machinery with fluid pipes

Limiting hydraulic system wear

All of those factors will help prevent component wear in the hydraulic system and may or may not work for the machinery you have. Which is why knowing the machine specifics along with the manufacturer recommendations are vital to prevent buying the wrong fluid. Hydraulic systems have gotten more advanced and efficient over the years as technology advances; so the fluid that is formulated to work on an older hydraulic system won’t protect your newer machinery.

The same can be said for the different types of systems; one may need a water emulsifier and another may need a demulsifier based on the way it operates. Those are both ways to remove the water from the hydraulic system (necessary) but both of those won’t work in every system.

Another important consideration is what type of environment the machinery will be operating in; all weather operations require a greater temperature range than a controlled environment would. This could also mean changing the fluid seasonally, if the temperature ranges are drastically different.


Choosing the right hydraulic fluid can be a somewhat challenging, yet it is very important to the life and operating quality of your heavy equipment and ultimately, your bottom line.

While it may seem a trivial detail that is easily glossed over, the devil is in the details in this case and it is worth finding the highest quality hydraulic fluid you possibly can. Not only to increase performance and lengthen the equipment life, but to prevent component wear as replacing the parts of the hydraulic system can be expensive.

On top of choosing the right hydraulic fluid based on the guidelines explained already, it’s important to stay on top of equipment maintenance; something that can easily be done with this scheduling service, where all the details for every machine are easily available.

By choosing the right hydraulic fluid and staying on top of a maintenance schedule, your heavy equipment will always be operating at the highest level it can, maximizing production and minimizing machine downtime.



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