What is meant by a multiviscosity oil?

• A. It has a fixed viscosity regardless of temperature.
• B. It is a lubricating oil with a viscosity index improver that increases the viscosity of the oil when hot and decreases the viscosity when cold.
• C. It is a blend used only for extreme cold environments.
• D. It is the same as synthetic oil.

Answer: (B)

Multiviscosity (multigrade) oil uses viscosity index improvers—special polymer additives—that adjust how the oil flows as temperature changes. At cold temps, the oil stays relatively thin for better cold-start and pumpability; as the engine warms up, the polymers uncoil and increase the oil’s resistance to flow, helping maintain a thicker, protective film. That’s why these oils are labeled with two numbers, like 10W-40: the first number describes cold-start behavior, and the second describes high-temperature viscosity. The idea described in the statement—an oil that decreases viscosity when cold and increases it when hot due to viscosity index improvers—best captures this behavior. It’s not about having fixed viscosity, it’s not limited to extreme cold, and multiviscosity oils can be mineral or synthetic, so it’s not the same as just calling it synthetic oil.