Base Number

The alkaline content of a lubricant may be measured and expressed as a neutralization number obtained from a base titration. Base Number BN or TBN – Total Base Number) measures the total alkaline content present in the lubricant. Many of the additives used in engine oils contain alkaline (basic) materials intended to neutralize the acid-forming processes of aging and fuel combustion. A relatively high BN is associated with increased protection against ring and cylinder liner corrosion and damage to “yellow” metals, such as copper and bronze. Abnormal decreases in BN indicate a reduced acid-neutralizing capacity and/or a depleted additive package. The test first determines the amount of acid required to neutralize the alkaline content of the sample. The final result is then expressed as an equivalent amount of potassium hydroxide per gram of sample.