Lubricant additives – detergents: In automotive engine oils, what is the primary function of the detergent additive system?

Introduction:
Modern engine oils contain additive packages that include detergents and dispersants to manage deposits, soot, and oxidation by-products. This question asks for the primary role of the detergent function.

Given Data / Assumptions:

• Context is multi-additive automotive engine oils.
• Detergents are typically metallic sulfonates, phenates, or salicylates.

Concept / Approach:
Detergents help neutralise acidic species and keep surfaces clean, while the overall detergent-dispersant system keeps contaminants finely divided and suspended so they do not plate out as deposits and can be transported to the filter or drained. Although antioxidants, corrosion inhibitors, and viscosity index improvers exist, those are different additive families.

Step-by-Step Solution:

Verification / Alternative check:
Oil datasheets and additive literature describe detergent/dispersant systems as central to piston cleanliness and sludge control.

Why Other Options Are Wrong:

• Reduce deposits by dissolving varnish only: Too narrow; detergents act earlier to prevent deposition and neutralise acids.
• Increase oxidation stability: Antioxidants do this, not detergents.
• Prevent rusting: Primarily corrosion inhibitors.
• Thicken the oil: Viscosity index improvers and base oil selection govern this.

Common Pitfalls:
Confusing the detergent function with antioxidants or VI improvers; in practice detergents and dispersants are paired but have distinct chemistries.

Final Answer:
Keep contaminants and insolubles in suspension for removal by flow/filters