Determining Acceptable Water Content in Motor Oils

Noria Corporation
Tags: motor oils

"What is the acceptable amount of water in 15W40, 5W20 and 5W30 motor oils?"

Keeping lubricants clean, cool and dry, and machines aligned, balanced and well-oiled is the foundation of reliability improvements in any lubrication program. While many people understand the clean part, which involves proper selection of filters and filtration methods, some struggle with the "dry" part of lubricants.

Before providing criteria to help you determine acceptable water content in your lubricants, let's first discuss why removing water is important.

Water ingression is the second most destructive contaminant and can wreak havoc in your system. Emulsified water is defined as microscopic globules of water dispersed in a stable suspension in the oil. Although all states of water in oil can cause damage to the oil and machine, emulsified water is considered the most destructive.

Water contamination also has a negative impact on the base oil of the lubricant and causes problems such as oxidation, hydrolysis and aeration. In oxidation and hydrolysis, water promotes changes in the chemical and physical properties of mineral oils and some synthetics, which lead to acid formation, viscosity change, varnish and sludge.

Another negative effect that water can have on equipment comes in the form of additive depletion. Additive polarity is defined as the natural directional attraction of additive molecules to other polar materials in contact with oil. These polar materials include water, a sponge, glass, dirt, a metal surface and wood pulp. In effect, additives take a ride on particles or water droplets.

Studies have shown that the amount of water you have in your lubricants (depending on temperature) can have a huge negative impact on equipment reliability.

Hopefully, you are now aware of why it's important to remove water from lubricants. Of course, the first step is to determine the equipment's criticality. How important is this piece of equipment to the whole process? Do you have standby or redundant equipment? What is the cost of the machine? What are your inventory levels?

The next step should be to determine the Optimum Reference State of the equipment. In other words, you need to know the best applications, modifications and additions that will help you reach lubrication excellence.

The final step is to apply the Reliability Penalty Factor (RPF) to your equipment (see the RPF chart below). After you have determined the RPF, simply follow the Dryness Table (listed below) and match your RPF with the specific machine.

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