Total Base Number (TBN) - Lubricating Oil Analysis
The total base number is an expression of the amount of alkaline additives in the lubricant that are capable of neutralizing the acid products of combustion.
A new oil starts with the highest TBN it will possess. During the time the lubricant is in service, the TBN decreases as the alkaline additives neutralize acids. TBN is an essential element in the establishment of oil drain intervals since it indicates whether the additives are still capable of providing sufficient engine protection.
Most diesel engine manufacturers require the oil drained when its TBN reaches one-half or one-third its original value.
Cause
• High-sulfur fuel
• Overheating
• Extended oil drain interval
• Improper oil type
Effect
• Increased acid no.
• Oil degradation
• Increased wear
• Corrosion of metal parts
• Acid build-up in oil
Solution
• Use low-sulfur fuel
• Follow manufacturer's recommendations for oil drain interval, and decrease if engine is operated under severe conditions
• Verify TBN of new product/use correct oil type
• Change oil/top off with fresh oil
• Test fuel quality
