Total Base Number
How does TBN differ from TAN (Total Acid Number)?
TBN measures alkaline reserve (acid-neutralizing capacity), while TAN measures acid buildup; rising TAN plus falling TBN indicates accelerated oil degradation.
What ASTM method measures TBN in new vs. used oil?
ASTM D2896 (potentiometric titration with perchloric acid) is standard for new oils; ASTM D974 is often used for used oils but may miss 'soft' TBN from amine additives.
Why is TBN threshold lower for heavy-duty diesel (~10 mg KOH/g) vs. gasoline engines (~7–8 mg KOH/g)?
Diesel combustion produces more sulfur-derived acids; higher TBN provides greater alkaline reserve to neutralize corrosive byproducts.
Can TBN rise in used oil?
Rarely; a rise may indicate additive contamination (e.g., mixing oils) or measurement error, but TBN almost always declines due to additive consumption.
What happens if TBN drops below 3 mg KOH/g?
Oil loses acid-neutralizing capacity, leading to corrosive wear, increased piston deposits, and potential bearing failure in diesel engines.
Total Base Number (TBN) is the alkaline reserve in lubricating oil, quantified as milligrams of potassium hydroxide (KOH) required to neutralize all basic constituents in 1 gram of oil (mg KOH/g). It represents the concentration of overbased detergents and amine additives that neutralize acids from combustion, critical for monitoring oil condition.
In ServiceGrid CMMS and asset reliability, TBN is a critical condition-monitoring metric for heavy-duty diesel and marine engines. Maintenance teams trend TBN via oil analysis to trigger oil change tasks when it drops to approximately 30–50% of initial value or reaches 3.0 mg KOH/g. This prevents corrosive wear and extends asset life by ensuring adequate alkaline reserve to neutralize sulfur-derived acids from combustion, reducing downtime and maintenance costs on the shop floor.
Ignoring TBN depletion until catastrophic corrosive wear occurs, such as piston ring or cylinder liner damage, by waiting for oil to turn black instead of trending alkalinity loss.
Over-reliance on TBN alone for modern low-sulfur fuel oils where additive chemistry shifts make TBN less predictive of remaining life, leading to premature or delayed oil changes.
Using inconsistent TBN thresholds across fleets, such as draining at 50% vs. 30% drop, without OEM-specific validation, causing inconsistent maintenance intervals and increased downtime.