Which is not the purpose of an additive?

• A. Reduce wear
• B. Improve lubricity
• C. Improve viscosity stability
• D. Color the lubricant

Answer: (D)

Additives are added to lubricants to boost performance, not appearance. They reduce wear by forming protective films on metal surfaces under load, which keeps surfaces from scuffing and avoids metal-to-metal contact. They improve lubricity by lowering friction between sliding parts, making motion smoother and reducing heat. They also stabilize viscosity over temperature changes, using viscosity-index improvers so the oil doesn’t thin out too much when hot or become too thick when cold. Coloring the lubricant, while sometimes done for identification or branding, does not enhance these protective or performance properties, so it is not a real purpose of an additive.