Lube Condition Indicators
Most modern lubes, particularly engine lubes, are "oxidation stable" under standard drain intervals so that, unless extended drains are contemplated, it is better to observe the contamination which influences viscosity rather than the viscosity itself. On the other hand, increased viscosity in the absence of solids or other contamination, will usually indicate lube problems.
Oxidation/degradation and viscosity are the most convenient means to measure this with reasonable effectiveness. Viscosity, along with Neutralization Number, should always be required by customers wishing to safely evaluate extended drain intervals for engines.
Neutralization Number
There are a variety of neutralization numbers utilized in the petroleum industry. This discussion is confined to the two most commonly used versions.
Total Acid Number (TAN): Simply stated, TAN is the amount of acid and acid-acting constituents found in the lube. The term "acid" does not necessarily connote metal corroding materials themselves. Many chemicals, including necessary lube additives, can have an acid number.
Significance: Increases in TAN of used lubes from the starting point of the new lube (which may not necessarily be zero) usually indicate lube oxidation or corrosive acid contamination.
