Acid Number (AN / TAN) and Base Number (BN / TBN) interpretation

TAN TBN Acid Number (AN / TAN) and Base Number (BN / TBN) interpretation

Acid Number – This is the concentration of acid in the fluid. The new oil value may not be zero since some oil additives react similar to acids with the reagents used for testing. Hence it is important to monitor the trend in change of TAN from a baseline sample or new oil reference. In engine applications this can be used in conjunction with a Base number value with the crossover of the two values a common method of deciding when to change oil. However, always be guided by your lubricant provider and OEM recommendations.

Base Number – This is the amount of alkali additive remaining in the engine lubricant. This is used in conjunction with an AN value and oil changes are typically either on a drop of 50% from a baseline sample or when the value becomes less than the AN. Again, always be guided by your lubricant provider and OEM recommendations.

Common Causes Potential Result Potential Advice

High Acid Number

And/or

Low Base Number

  • Overheating
  • Excessively extended drain interval
  • Wrong lubricant
  • High sulphur fuel
  • Decreased BN
  • Corrosion
  • Oil Thickening and Sludging
  • Increased wear
  • Filter blocking
  • Component Seizure
  • Evaluate oil drain interval.
  • Establish new baseline BN / AN values.
  • Change oil
  • Submit fuel sample for analysis
  • Submit coolant for analysis

 

High Base Number
  • Wrong oil added / topped up.
  • Cylinder oil contamination.
  • High Ash (SAPS) production
  • Wasted cylinder oil.
  • Reduce Cylinder oil fuel rate
  • Confirm correct lubricant in use.