Mixing of different types of oils is described as which of the following?

• A. Prohibited
• B. Permitted
• C. Not recommended
• D. Required

Answer: (A)

Mixing different oils is prohibited because each oil type is formulated with a specific base stock and additive package to meet exact engine or system requirements. When you blend oils, the resulting mixture can change viscosity and film strength, and additives can interact in unpredictable ways, potentially negating protective properties. This can lead to inadequate lubrication, increased wear, sludge or varnish formation, foaming, and other issues that compromise reliability and safety. For these reasons, maintenance manuals require that different oil types not be mixed. If oils of different types are found together, the correct procedure is to drain and refill with the proper oil to restore the system to specification.