TAN (Total Acid Number) and TBN (Total Base Number) oil analysis are used to determine how oils change as they age and when they should be replaced. These values are critical for assessing the oil's oxidation level, service life, and protection ability.

**TAN (Total Number of Acids):**
- TAN determines the total concentration of acidic components of an oil. As the oil is used, the amount of acidic components increases due to oxidation and thermal degradation. Therefore, the TAN value is considered an indicator of the level of oxidation of the oil.
- TAN is usually measured by the potentiometric titration method.

**TBN (Total Base Number):**
- TBN indicates the total amount of acidic components an oil can neutralize. Basic additives are added to engine oils to neutralize acidic components from fuel combustion products. The TBN is used to determine how long the oil can neutralize these acidic components.
- TBN is usually measured by the potentiometric titration method.

**Analysis Methods:**
- **ASTM D664:** is a standard test method for TAN.
- **ASTM D4739:** is a standard test method for TBN.

While the TAN of the oil increases over time, the TBN value generally decreases. If the TBN drops below a certain threshold, it may indicate that the oil needs to be changed. The TAN and TBN values provide critical information about the oil's ability to protect, its oxidation state, and whether it should be replaced. This type of analysis can help protect engines and equipment and reduce maintenance costs.