Why TBN And TAN?

By LEWIS FOX

In recent weeks, we have received many inquires on why our commercial reporting options offer both TBN and TAN. In an effort to explain our reasoning, we sought out one of the industrial leaders in maintenance, Mr. Lewis Fox.

What is TBN (Total Base Number): It is a measurement of the alkalinity remaining in the engine lubricant and is indicative of the oil’s ability to counteract acid formation. Decrease in TBN affects the ability of the lubricant to protect against corrosion of such engine parts as rings and cylinder liners. A low TBN usually means a low dispersion characteristic and a depleted additive package.

What is TAN (Total Acid Number): TAN represents all acidic constituents in a lubricant, including those from certain additives, combustion blow-by and oxy-materials. It indicates acidic contamination of the oil or increased oil oxidation, both of which raise the potential for corrosive wear.

Because the chemistries used to make up TBN can differ in quality and ability to maintain effectiveness over extended drain intervals, the TAN test and results is the most accurate measure of the oils on going ability to resist degradation from greater level of acidity. This definitely makes the TAN test the preferred test method for used oil analysis when determining extended drain capabilities of a wide variety of oils.

With TBN, industry standards will generally recommend a drain of the oil when the TBN has been used up….generally about ½ of its original number. For TAN, as the acid level increases to about double of the oil’s original TAN, generally a drain of the oil will be called needed. The original TAN level varies from type of product (Hydraulic Oil, Transmission Fluid, Engine Oil, etc.) as well as varying from manufacture to manufacture. For engine oils, an upper limit of 5.0 is often used as a condemnation limit.

On a global scale, industry standards have determined an oil with a TBN of 9 or 10 is generally all that is necessary to meet the various API and engine manufacture’s specifications. There are brands of oil on the market with much higher TBN’s available. With the introduction of EGR (Exhaust Gas Recirculation) engines, some OEM’s engine manufactures are calling for a slightly higher TBN such as 11 or 12. In a few European countries, where sulfur content of the fuel may be extremely high, a TBN of 11 or higher may be suggested. In these isolated incidents, it is important to keep in mind a high TBN rating of one oil over another is not always an advantage.

A key factor is not necessarily how high the TBN rating is, but what is the quality and retention capability of its chemistry, especially over extended drain interval periods.

An oil analysis of your new oil will determine a base line for extended drain choices. It is important to know the starting point of any oil before determining the periods of your extended drain program.

For more information on extending drain intervals of your equipment, kick us an email and we’ll send you our special report titled “Using TBN & TAN Numbers to Extend Drains”.

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