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Choosing Heavy Equipment Hydraulic Oils

Choosing the hydraulic oil that best suits a fleet can be as confusing as selecting one sandwich from a take-out menu to feed 25 people, not an easy task as it has to fit the budget and satisfy many different tastes. This selection process has gotten progressively complicated over the past few years due to performance, service life, higher pressures, wet-brakes, OEM warranty, etc. For the equipment manager trying to decrease costs per hour, maintaining these complex systems, using a single hydraulic fluid has become increasingly difficult.

So what are the types of fluid available? There are two basic types of fluid commonly used in heavy equipment hydraulics. Both types are engineered to perform the same functions………right? The oils have several key functions: transmit power from operator control valves to work implements, lubricate critical hydraulic components, and provide cooling to the hydraulic system. It sounds simple, but in reality, for fleets that represent many different types of equipment and several different manufacturer brands, selecting a single hydraulic fluid is a tall order.


Several OEM’s hydraulic oil specifications require higher levels of zinc and additional additives that are similar to those found in engine lubricants.  This type of fluid typically has high viscosity indexes, meaning they react very well to higher temperatures and provide robust film strength between moving parts. The engine oil additives also have high detergency and can prevent varnishing and are resistant to oxidation. These fluids, due to their engine oil formulation, also emulsify water allowing the oil to absorb the moisture and preventing “free water” from accumulating in the system. Why is this attribute so important? Water is heavier than the lubricant, and will settle out in hydraulic oil reservoirs and typically rest near the suction pipe. This free water can be very damaging to hydraulic components especially during start up when the pump creates suction and pulls the water through the system.  Water can sometimes be unavoidable, but is much less damaging if smaller amounts are absorbed within the lubricant, rather than separating from the fluid.


AW, or anti-wear, type fluids have their own uses in commercial heavy equipment  in systems designed for this type fluid, most commonly where the hydraulic system is segregated to hydraulic components only, such as excavators, skid steer loaders and other machines that do not have clutch or brakes discs operating in the common sump. These fluids tend to have lower price points than the engine oil type fluids and are readily available. This type lubricant can have extended service life in systems that operate at high pressures as the oil is resistant to aeration and foaming. These AW fluids are also offered with high viscosity indexes, as well as environmentally friendly formulations where applications require a fluid or a lubricant of this type.

So what is the perfect single type fluid for a fleet? There is not one single answer for every fleet, and in some cases there is not a single fluid that can meet all the OEM requirements, while providing the best service life, performance, and consolidation required by the equipment manager.  The correct action plan is to contact a lubricant professional to review the equipment and determine the best type fluid that can meet the needs of each operator.  Kind of like that that single sandwich that 25 people can agree upon.

Bon Appetite!


Greg Wyatt is a Certified Lubricant Specialist at PetroLiance and enjoys creating custom lubricant solutions for clients in the Commercial Vehicle, Transportation and Construction & Mining Industries.  Contact Greg, or any Lubricant Specialist at PetroLiance with your Industrial Lubricants, Fuels and Hydraulic Oils technical questions.