Moisture Contamination in Engine Lube and Hydraulic Oil

Water is one of the most common contaminants in a lubricating fluid system and also one of the most damaging. In lower temperatures, moisture or water in hydraulic systems can be a serious problem. The hydraulic fluid has less ability to hold moisture as the freezing point of water is reached (32oF/0oC). As the temperature decreases below the freezing point, ice crystals form, adversely affecting the function of the entire system.

Testing for water

Laboratory analysis

To determine if water is present, a fluid sample can be analyzed and tested in a laboratory. A report will be provided with the actual amount of water present in parts per million (ppm).

On-site testing

There are two simple ways to determine on-site if engine oil or hydraulic fluid contains water:

1) Look at the system and if the fluid is milky in the area of the breather or fill cap/dipstick, more than likely there is moisture above the normal saturation point.

2) Use a simple crackle test to check for moisture in the lube or hydraulic system. Put a small amount of oil on a piece of tin foil, in a spoon or in a small metal container. Hold a small flame under the foil/spoon/container containing the fluid. If moisture is present then the fluid will crackle and pop as soon as it is heated up.

On-site analysis using the above methods will not determine the actual content of water, only if water is present. If actual water content is required, laboratory testing will be necessary.

Removing water

For excess water in the hydraulic fluid, there are several methods for removing free (unstable suspension) and emulsified (stable suspension) water including:

Polymeric filters  

Polymeric filters look like conventional particulate filters, however, the media is impregnated with a super-absorbent polymer. Water causes the polymer to swell, trapping the water within the media. Parker Racor Water Removal polymeric filters, are best suited for removing small volumes of water and/or maintaining water contamination within pre-determined limits.

Vacuum distillation

Vacuum distillation employs a combination of heat and vacuum to remove water from hydraulic fluid. At 25 inches Hg, water boils at 133°F (56°C). This enables water to be removed at a temperature that does not damage the oil or its additives. Depending on the application, the Parker PVS Portable Purification System or the Sentinel Compact Oil Purifier provide protection from water contamination for applications with larger volume hydraulic and lube oil systems.


Dehumidification involves circulating and dehumidifying air from the reservoir headspace. Water in the oil migrates to the dry air in the headspace and is eventually removed by the dehumidifier.  Dehumidification systems are used in applications where there are large volumes of hydraulic or lube oil and have moisture present which is caused by high humidity in the reservoir.

Preventing water contamination

In many situations, it is more economical to prevent water from entering the hydraulic fluid system than it is to remove water from the fluid once it has been introduced. A Parker Racor Absolute Bypass filtration system, or Parker Hydraulic Oil Conditioning Unit, (OC2)  installed upstream of critical system components will ensure contaminant-free fluid and prevent damage due to minimum amounts of moisture and other contaminants. The OC2 is a complete filter, pump and motor assembly which can be connected to a sump and can clean fluid whether the machine is running or not.

For more information on fuel, air, and oil filtration systems for engines and fuel delivery, contact Parker Engine Mobile Original Equipment Division.


This post was contributed by the Engine Mobile Filtration Team.

Related Posts:

Clean Hydraulic Fluids Are the Key to Top Performance

Reduce Failure of Hydraulic Systems with Preventive Maintenance

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