Industry rides on a film of oil. The oil’s viscosity bears the load and defines the extent of clearance achieved between working surfaces. Sometimes that clearance is thick and bountiful, and other times it is deflated or extinct. Without viscosity, most machines would rapidly self-destruct with mechanical friction and wear.

There is also a well-known penalty and reliability risk from too much viscosity. Like most things, the selection of a lubricant’s viscosity must be optimized to enable needed protection and disable the danger from excessive viscosity. For instance, too much viscosity can cause churning losses and excessive heat generation from molecular friction. It can also impede lubricant movement and flow to lubricant-hungry surfaces.

One of the most famous disadvantages of too much viscosity is high energy consumption. In recent years, we’ve seen automaker-specified viscosity being lowered in crankcase service from 5W40 to 5W30, and now in some cases to 5W20. These changes are all for the sake of energy conservation.

Of course, the primary driver for energy conservation is not to save money on fuel or electricity but rather to reduce the consumption of fossil fuels, which emit harmful gases (carbon dioxide, nitric oxides, hydrocarbons, etc.) into the atmosphere as a byproduct of combustion.

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Too often the viscosity index (VI) is disregarded as a lubricant selection parameter. One reason is simply because it is poorly understood. Some people think the viscosity index is incorporated in the ISO Viscosity Grade, but it is not. It stands alone as an independent lubricant performance differentiator.

We all know that viscosity is the single most important physical property of a lubricant. It is a crude measure of a lubricant’s molecular constitution from the standpoint of hydrocarbon chain size. Viscosity is determined by creating friction between the molecules from fluid movement. The higher the intermolecular friction (longer molecular chains), the higher the viscosity.

Viscosity determines film thickness and film strength in machines. It also influences other important factors such as those in the table below.

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It takes only a small amount of water (less than 500 ppm) to substantially shorten the service life of rolling element bearings. There is a vast amount of research that supports this. Being a career-long crusader of clean and dry oil, I will certainly not argue the contrary. In fact, water’s destructive effects on bearings can easily reach or exceed that of particle contamination, depending on the conditions.

My theme for this column, therefore, is not about whether water imparts harm but rather how it does. Knowing how water attacks and causes damage helps in setting important dryness targets and also aids failure investigations post mortem. Further, when water contamination is unavoidable, understanding these water-induced failure modes can be valuable in the optimum selection of lubricants, bearings and seals for defensive purposes.

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You may be surprised to learn that there are no less than five lubrication performance properties that are missing from nearly all in-service oil analysis reports. These are not esoteric properties that are of limited value or interest to those in charge of machine reliability. Instead, they represent the core foundation of a lubricant’s formulation and purpose. In other words, they relate to the essence of what we expect and need from a lubricant. And, these are the properties that are imparted by additives and commonly found on a lubricant’s product data sheet (spec sheet).

Don’t get me wrong; I am not suggesting that commercial oil analysis labs are duping their clients by shortchanging testing services. Many of these missing tests cannot be practically performed on routine oil samples because they are expensive, involve prolonged test periods and/or require large sample volumes. Yet it is important that the user community fully understand what they get and what they don’t get when they pay $35 for oil analysis.

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