Total Base Number (TBN)

Last updated: November 4, 2018

What Does Total Base Number (TBN) Mean?

Total base number (TBN) refers to the quantity of acid, expressed in terms of the equivalent number of milligrams of potassium hydroxide required to neutralize all basic constituents present in 1 gram of sample.

TBN determines the effectiveness of the control of acids formed during the combustion process. The higher the TBN, the more effective it is in suspending wear-causing contaminants and reducing the corrosive effects of acids over an extended period of time.


Corrosionpedia Explains Total Base Number (TBN)

Total base number is a property generally associated with engine oils. It is the oils' ability to neutralize acid. The higher the TBN, the more acid it is able to neutralize. This quality is also referred to as alkaline reserve and is directly proportional to the amount of active detergent contained in the oil.

New engine oils typically possess TBNs from 5.0 to 15.0, depending on manufacturer and intended service. As the oil is used, it becomes contaminated with acids and the TBN drops. Generally, TBN levels below 3.0 are considered too low and indicate that the oil should be changed in order to maintain good engine health.

One cause of TBN depletion is the use of low-quality, high-sulfur fuel. During the combustion process, this sulfur turns to sulfuric acid and in turn, accelerates TBN depletion. Overheating and over-extended drain intervals can cause oil oxidation. The products of oxidation are acidic and cause the TBN to drop. Therefore, fuels containing a higher amount of sulfur decrease the TBN more quickly due to the increased formation of sulfuric acid.


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