What does TBN mean for engine oil?

The abbreviation TBN stands for the Total Base Number. The TBN indicates the amount of alkaline additives present in the oil. In this context experts also speak of the alkaline reserve of engine oil. It is described how much acid can be neutralized.

Lubricating oil should not develop an acidic pH value in order to remain stable and functional for a long time. If the oil becomes too acidic due to the introduction of foreign substances, oil ageing and the decomposition of the lubricant is accelerated. The oil would have to be replaced promptly.

By adding additives it is possible to provide the oil with an alkaline reserve. This neutralizes acids in the oil and it remains usable for longer. In the case of engine oils, for example, the acidic combustion products in the oil are thus neutralized.

The TBN gives important information about the remaining life of the oil in case of used oil. If the TBN matches the TAN too closely, an oil change is necessary. The alkaline reserve should always be higher than the acid input.

The TBN is determined by the ASTM D2896 method using a titrator. By titration the TBN is given in mg KOH/g oil.

What is the TAN?

The TAN is also known as the Total Acid Number. It defines the quantity of acidic substances in 1g of a sample of the lubricant. It is determined by titration with ethanolic potassium hydroxide solution according to ASTM D664. The amount consumed is expressed in mg KOH/g. The TAN is mainly determined for used oil by oil sampling to determine whether the oil is still usable or too acidic.

What TBN does engine oil normally have?

The TBN is an important parameter for engine oils, as they are exposed to a particularly strong acid input due to combustion residues. Fresh gasoline engine oils have a TBN of 6-13 mg KOH/g.

Institutions such as ACEA also issue limit values for their releases, which the TBN must not fall below. In ACEA classes C3, C4 and C5 it was specified that the TBN must be ≥ 6.0. For ACEA A3/B3 and A5/B5 the TBN is always above 8.0. An engine oil with ACEA A3/B4 approval requires a TBN ≥ 10.0.

Examples of lubricants by ADDINOL

We have collected some examples of our engine oils and indicated the corresponding TBN.


Heiko Stephan

Share this post