Low ash and ashless additive in motor oil

Low Ash type detergent/dispersants are used in most motoroil including the 2-strokes.

These detergents are manufactured from compounds of Calcium and Magnesium (heavy metals). After these compounds (Calcium Phenate or Magnesium Phenate) do their job, they burn away, forming a heavy metal salt (ash) that is swept away during the normal combustion process. Hence, this is where the name Ash-type detergent comes from.

As antiwear agent: The added Zinc compounds (Zinc Dithiophoshate) flow in with the oil and are not much used unless the base oil breaks down. If the base oil breaks down, they form a protective barrier between the moving parts (usually piston skirts and cylinder walls).

Some manufacturers are using a combination of detergent types (Ashless and Low Ash) to provide a broader range of uses for their oil and extend oil drain.