This tutorial is intended to familiarize the oil analysis user with the various tests performed on used oil and the implications of the results to maintenance personnel.
Today's lube oil is expected to perform many functions during its useful lifetime. During usage, it changes physically and chemically according to conditions dictated by the lube system. These changes alter the lubricating characteristics of the oil, eventually rendering it unsuitable for use. Therefore, to evaluate the used oil it is important that we first understand the functions it is expected to perform. The functions are explained below:
Control Friction: Moving parts of the lube system are separated by a film of oil which reduces the force needed to keep those parts in motion.
Control Wear: This function is closely related to friction control, in that oil and additive film between moving engine parts acts as a medium to reduced metal to metal contact, and consequently, wear.
Control Contamination: Contaminants such as fuel, dirt, hard wear metals and solids are removed from lubricated componants by flushing or washing action of the oil.
Control Corrosion: Detergent and dispersant additives in lube oil act to surround and neutralize any acids formed during the fuel combustion and or oil oxidation processes.
Control Temperature: Heat is carried away from the high temperature regions of the lube system to the cooler.
Reasons for Lube Failures |
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Contamination from Outside Sources
Contamination of lube oil, whether it be from fuel, dirt, water, fuel soot, or some other source, is the primary reason an oil fails to do it's job. Contamination can be detected by lab analysis and must be controlled by maintenance procedures.
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Loss of Lube Properties Provided by Oil Chemistry (Oil Breakdown)
Today's high quality lube oils are formulated with chemical additives which enhance lubrication performance. These additives disperse sludge, neutralize acid, reduce friction, maintain more uniform viscosity, lower pour points and perform a variety of other functions. However, each additive is limited as to its usefulness. For example, the detergent additive in one quart of oil can only neutralize so much acid formed by fuel combustion. When that additive is used up, the oil must be replaced or acid corrosion will result.
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The Value of Used Oil Analysis
Physical and chemical tests are available to analyze used lube oil. These tests can pinpoint levels and sources of contamination and quantify any loss of oil additives. This information, in the hands of maintenance personnel, provides an effective way to "look" inside the lube system and "see" what type of wear is taking place. Since the oil carries all particles of lube system wear, one can effectively pinpoint any excesses through analysis of types and quantities of metal found in the sample. |
