Abstract: The stability of diesel engine oil additives is investigated with several methods associated with sediment and particle. Study shows that overbased calcium alkylbenzene sulfonate is found to have the most sediment and the largest particle diameter. A lot of sediment is found when overbased calcium alkylbenzene sulfonate mixes with overbased sulfurized calcium alkylphenolate because forming larger particles through collision of the small particles,resulting in unstable colloid system, but no interaction is occurred. The addition of ashless dispersants makes the overbased calcium alkylbenzene sulfonate more stable becaused of the space steric effect of the dispersant.

Key words: additive, stability, colloidal structure, interaction