Total base number, in mg KOH/g, measured by ASTM D2896 or D4739. It comes mainly from overbased detergents and is highest in diesel and marine engine oils, from about 10 in road diesel oils to 40 or more in marine cylinder oils burning high-sulfur fuel. TBN falls as acids are neutralized; a drop to about half of new, or the point where TAN and TBN cross, is the usual drain signal.
TBN's at 4 on an oil that started at 11, we're past half, pull the drain forward.
Also heard as
- base number
- BN
Related terms
TAN
Total acid number: milligrams of potassium hydroxide needed to neutralize the acids in one gram of oil.
Detergent
Metal-based additive that keeps hot engine parts clean and neutralizes acids from combustion.
Oil analysis
Lab testing of in-service oil samples to judge oil condition, contamination and machine wear.
Additive package
Pre-blended mix of performance chemicals that a blender adds to base oil to make a finished lubricant.