Page 214 - An Introduction To Predictive Maintenance

204 An Introduction to Predictive Maintenance

ignition problems, improper timing, or other deficiencies may cause it. Fuel dilution
is considered excessive when it reaches a level of 2.5 to 5 percent.

Solids Content
The amount of solids in the oil sample is a general test. All solid materials in the oil
are measured as a percentage of the sample volume or weight. The presence of solids
in a lubricating system can significantly increase the wear on lubricated parts. Any
unexpected rise in reported solids is cause for concern.

Fuel Soot
Soot caused by the combustion of fuels is an important indicator for oil used in diesel
engines and is always present to some extent. A test to measure fuel soot in diesel
engine oil is important because it indicates the fuel-burning efficiency of the engine.
Most tests for fuel soot are conducted by infrared analysis.

Oxidation

Oxidation of lubricating oil can result in lacquer deposits, metal corrosion, or oil thick-
ening. Most lubricants contain oxidation inhibitors; however, when additives are used
up, oxidation of the oil begins. The quantity of oxidation in an oil sample is measured
by differential infrared analysis.

Nitration
Nitration results from fuel combustion in engines. The products formed are
highly acidic, and they may leave deposits in combustion areas. Nitration will
accelerate oil oxidation. Infrared analysis is used to detect and measure nitration
products.

Total Acid Number (TAN)
The acidity of the oil is a measure of the amount of acid or acid-like material in the
oil sample. Because new oils contain additives that affect the TAN, it is important to
compare used oil samples with new, unused oil of the same type. Regular analysis at
specific intervals is important to this evaluation.

Total Base Number (TBN)
The base number indicates the ability of oil to neutralize acidity. The higher the TBN,
the greater its ability to neutralize acidity. Typical causes of low TBN include using
the improper oil for an application, waiting too long between oil changes, overheat-
ing, and using high-sulfur fuel.