Answer is: Dispersants
Step-by-step explanation:
Dispersants keep contaminants (e.g. soot) suspended in the oil to prevent them from coagulating. Anti-foam agents inhibit the production of air bubbles and foam in the oil which can cause a loss of lubrication, pitting, and corrosion where entrained air and combustion gases contact metal surfaces.
So that's why the answer is: Dispersants