Base Number

Definition

Base Number measures a lubricant's alkaline reserve, or ability to neutralize acid. When Acid Number and Base Number approach the same number, the oil should be changed or "sweetened" (new oil should be added).

Standard Test Method Used

mod. ASTM D4739

Reporting Measurement

mg KOH/g (milligrams potassium hydroxide per gram of sample)

Amount of Sample Needed

4g

Test Limitation

Used for used engine oils only to determine safe extension of drain intervals. Contamination by coolant can artificially raise TBN.

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