A metal-containing additive, usually a calcium or magnesium sulfonate, phenate or salicylate, that keeps pistons and ring grooves free of deposits and neutralizes acids from combustion. Overbased detergents carry extra alkaline reserve, which is what TBN measures. Together with dispersants, detergents are why diesel engine oil turns black fast: soot is held in suspension instead of baking onto parts. They are kept out of turbine oils because they hold water in emulsion.
TBN's down to 3 from 10, the detergent's spent and the acids are going to start on the bearings.
Also heard as
- metallic detergent
- overbased detergent
Do not mix it up with
- Dispersant: Detergents clean hot surfaces and neutralize acid; dispersants hold soot and sludge particles suspended in the oil itself.
Related terms
Dispersant
Ashless additive that keeps soot, sludge and oxidation products suspended so they drain out with the oil.
TBN
Total base number: the alkaline reserve left in an engine oil to neutralize combustion acids.
Additive package
Pre-blended mix of performance chemicals that a blender adds to base oil to make a finished lubricant.
Elemental analysis
Spectrometric measurement of wear metals, contaminants and additive elements in oil, in parts per million.