is noncombustible residue of a lubricating oil or fuel,
determined in accordance with test methods ASTM-D-482 and
D-874 (sulfated
ash). Lubricating oil detergent additives contain metallic derivatives, such
as barium, calcium, and magnesium sulfonates,
that are common sources of ash. Ash deposits can impair engine efficiency
and power.
Also see detergent.