Question 86Motor Plants - QMED

The correct answer is C) form a protective film on metal surfaces. Corrosion inhibitors and/or soluble oils are added to diesel engine cooling systems to form a protective film on metal surfaces. This helps prevent corrosion and pitting of the metal components within the cooling system, which can otherwise occur due to the chemical reactions between the cooling water and the metal. The other answer choices are incorrect because they do not accurately describe the primary purpose of adding these additives. Reducing cooling water temperature (A), increasing cooling water hardness (B), and maintaining low pH in the cooling water (D) are not the main reasons for using corrosion inhibitors and/or soluble oils in diesel engine cooling systems.