What additive is used in engine oil to neutralize acids?

The correct choice is detergent. In engine oils, detergents serve a crucial role by neutralizing acids that can form during the combustion process. These acids can arise from fuel combustion and oil oxidation, potentially leading to corrosion and damage to engine components if not properly managed. Detergents contribute to maintaining the cleanliness of engine parts by preventing deposits from forming and ensuring the oil remains effective in its protective functions.

Using additives like detergents helps in maintaining a balanced pH level within the oil, mitigating the harmful effects of those acids. This proactive approach enhances engine longevity and overall performance, showcasing the importance of proper lubrication and additive use in engine maintenance.

The other options do not serve the function of neutralizing acids. Rust inhibitors prevent oxidation and rust formation, demulsifiers help in separating water from oil, and anti-wear additives create a protective layer on surfaces to reduce friction and wear. Each additive type has its specific role within lubricants, but only detergents are specifically designed to neutralize acids.