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What to Look for in Hydraulic oil; Reviewing Hydraulic Oil Standards

What to Look for in Hydraulic oil; Reviewing Hydraulic Oil Standards

The next time you enter a vender’s shop for some hydraulic oil, you’d better consider your choices first. Any mistake with oil can spell Danger to your hydraulic system and equipment in general. And that is exactly why we, Stretched Perfections, are giving you this free guide to choosing the best oil for your equipment.

The baseline is that if you use any oil with the different standards from what your machine needs, chances are that it won’t serve you as it should. You don’t want that, do you? Now let’s get rolling.

Viscosity is King

Am imagining of a heavy oil, something between solid and liquid. Combine that with the snowfall and you surely know that you’ll be starting your engine forever. My point is that you need to get the right viscosity for your hydraulic system, may it be oil or any other fluid.

Get these right. Choose oil viscosity depending on the type of equipment you are operating, its operating environment, and the kind of work it does. But more important is the mechanical and volumetric efficiency needed for the equipment. High viscosity causes a drop in mechanical efficiency but raises volumetric efficiency. And the vice versa is true of course.

First, check the manufacturers’ guide for oil application specifications in your equipment. They know what works best with their products. ISO grades are another thing; never ignore them. They mainly indicate the viscosity and temperature range of the hydraulic oils and fluids.

Move with the weatherman. Cold weather will cause the hydraulic fluid to thicken, or rather to grow more viscous. You’ll definitely need some thin (not much thin though) oil to start the engine. In hot weather, the viscosity will reduce, and the fluid will flow more easily. But don’t take it kindly. A very thin fluid will leak easily through any aperture.

Hydraulic oil viscosity and temperature are one thing. If the hydraulic system gets too hot, the hydraulic oil reduces its viscosity greatly, while low temperatures boost the viscosity. The Society of Automotive Engineers (SAE) classifies oils in a VI scale table to show different viscosities depending on the temperature range.


Index Viscosity
0-350C Low
35-800C Medium
80-1100C High
1100C or more Very high

The viscosity and temperature indices are always labelled in the format 10W-40, but the numbers will differ.

Choice of additives           

Additives give hydraulic oil its various properties. The main additives include anti-oxidants which reduce sludge deposits and allow a longer use of the oil; anti-rust additives lessen the formation of rust in the components by forming a protective layer over the metallic parts.

For the winter, cold flow additives allow the use of the equipment under extremely cold weather. Anti-foaming additives cut foaming within the fluid thus reducing the equipment’s risk of damage. Finally, anti-wear additives simply moderate wear and tear in the hydraulic system and components.

Identifying the additives used

Watch out for these descriptions on container labels. They indicate the types of additives used.

HL represents refined mineral oils that have anti-oxidants and anti-rust properties.

HM stands for hydraulic oils with properties same to HL, but with added anti-wear features.

HR represents oils with properties similar to HL, but with additional VI improvers.

In a nutshell

Be considerate of your hydraulic system needs when choosing a hydraulic fluid or oil. There are many factors to consider of course, but they all rotate around viscosity and the additives used. Be sure to consider these. And don’t you forget to look into your system builder’s manual.

Work with the best manufacturer in the market: Stretched Perfections welcomes you to try our unique hydraulic products. Reach out to us through our contact page at any time.

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