Home Service Oil Company
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What Is Hydraulic Fluid and Why Is It Important?

May 12, 2021

From assembly lines to your favorite roller coaster and the brakes in your car, hydraulic systems can be found everywhere if you look closely enough! These amazing systems help plow the snow that accumulates on roads in the winter, allow us to brake behind the wheel at red lights, and ensure that airplanes work correctly and complete their journeys safely. While the components that make up these hydraulic systems should be celebrated, they would be practically worthless without one crucial part: hydraulic fluid. What exactly is hydraulic fluid? What does it do and why should you care? Learn all about this unsung hero and how it affects our daily lives!

What Is Hydraulic Fluid?

Hydraulic fluid is the very lifeblood that makes countless mobile and stationary machines work correctly. Without it, brakes would fail, transmissions can become destroyed, and engines’ lives would be greatly shortened. Made up of an amalgamation of fluids including water, water-oil emulsions, and salt solutions, hydraulic fluid serves multiple purposes in a hydraulic system.

There are three types of hydraulic fluids:

  • Water-based fluids: Perhaps the least common type of the three, water-based fluids are needed where there is a high probability of a fire occurring. Their downfall is they aren’t terribly great when it comes to lubrication.
  • Petroleum-based fluids: This mineral-based fluid is frequently used to offer pumps and other system pieces better lubrication, stability, and corrosion resistance. They do have the tendency to build up sludge, however, which can worsen the machine’s performance.
  • Synthetic fluids: These man-made hydraulic fluids are designed specifically for providing exceptional fluid stability, lubrication, and more. They work perfectly within a wide range of temperatures and even under high pressure. Their disadvantage? They’re costly, more toxic, and may be incompatible with standard sealing materials.


What Does Hydraulic Fluid Do?

The hydraulic fluid wears many metaphorical hats. While it’s mostly responsible for providing energy transmission through the system (which helps the machine do its job), hydraulic fluid also provides lubrication to reduce friction, dissipates and transfers heat to keep parts cool, seals clearances, and helps prevent corrosion and contamination. A quality hydraulic fluid helps make any hydraulic system work as efficiently as possible!

Why Not Just Use Water?

Okay, we get where you’re going. Hydraulic fluid and water are both liquids – so why not just use water? In the past, people used water in earlier hydraulic systems but soon stopped because so many problems arose. Water is a touchier fluid and will evaporate or freeze much more easily than hydraulic fluid. Also, since it is an electrolyte, water will lead to rusting inside the lines as soon as air leaks into the system, which leads to corrosion. It also isn’t a great lubricator between moving parts. Hydraulic fluid addresses all these issues!

Are Hydraulic Fluid and Hydraulic Oil the Same?

You might hear these two terms used interchangeably, but beware! They’re not exactly the same thing. Hydraulic oil is a flammable fluid designed to transmit power while acting as a coolant and lubricant; however, it isn’t suitable for using close to an ignition source. On the other hand, hydraulic fluid consists of various fluids (including plain ol’ water) and can be used more widely in automobile systems, where volatility (and the possibility of a fire) is present.

What Should You Look for in a Good Hydraulic Fluid?

There are a few key factors you should look out for when you’re in need of a good hydraulic fluid. Here are the top 4 characteristics you should consider:

  • Viscosity: This is absolutely essential! If the viscosity is too low, your machine’s components may suffer from excessive wear and tear. If it’s too high, your system’s performance can become sluggish and less efficient. It needs to be juuuuust right.
  • Viscosity Index: This seems similar to viscosity, but it’s not the same, so please don’t disregard this factor! The viscosity index (VI) shows how various temperatures affect the fluid’s viscosity. High VI fluids work perfectly when temperatures fluctuate or when extremes occur (like in that brutal polar vortex that plunged the nation into dangerously cold temperatures in 2014).
  • Oxidation stability: Oil + oxygen = oxidation, which greatly reduces the life of a fluid and leaves behind sludge and varnish. Bottom line: oxidation will harm your hydraulic system. Make sure that your fluid can take the heat and resist oxidation!
  • Wear resistance: This will tell you about the fluid’s ability to reduce the wear rate in areas that introduce friction. If your hydraulic fluid is equipped with anti-wear additives, you should be in good shape!


Count on HSO for Your Hydraulic Fluid Needs

Home Service Oil is proud to carry all types of lubricants for your vehicles, trucks, off-road equipment, and more. From hydraulic fluids to synthetic oils, coolants, and everything in between, we’ve got it all. Not sure which type of hydraulic fluid you need? We can help you choose the right one! Contact us online or call us at 1-800-467-5044 to learn more!