Which statement about multiviscosity oils is true?

Which statement about multiviscosity oils is true?

• A. They have a fixed viscosity regardless of temperature.
• B. They do not require viscosity index improvers.
• C. They contain a viscosity index improver to vary viscosity with temperature.
• D. They are identical to ashless dispersant oils.

Answer: (C)

Multiviscosity oils use a viscosity index improver to shape how their thickness changes with temperature. These additives are long polymer molecules that behave differently as temperature shifts. At cold temperatures, they stay relatively uncoiled and don’t add much to viscosity, so the oil flows more easily for good cold-start protection. As the engine warms up, the polymers unwind and entangle, increasing the oil’s viscosity so it can still provide adequate lubrication at operating temperature. This is why multi-grade oils are labeled with two numbers (like 5W-30): a low cold-temperature number for starting flow, and a higher hot-temperature number for protection. Without viscosity index improvers, the oil’s viscosity would swing too much with temperature and wouldn’t meet the multi-grade specification. Ashless dispersant oils, on the other hand, are designed to keep contaminants suspended, not to control temperature-dependent viscosity, so they’re not the same thing.

Multiviscosity oils use a viscosity index improver to shape how their thickness changes with temperature. These additives are long polymer molecules that behave differently as temperature shifts. At cold temperatures, they stay relatively uncoiled and don’t add much to viscosity, so the oil flows more easily for good cold-start protection. As the engine warms up, the polymers unwind and entangle, increasing the oil’s viscosity so it can still provide adequate lubrication at operating temperature. This is why multi-grade oils are labeled with two numbers (like 5W-30): a low cold-temperature number for starting flow, and a higher hot-temperature number for protection. Without viscosity index improvers, the oil’s viscosity would swing too much with temperature and wouldn’t meet the multi-grade specification. Ashless dispersant oils, on the other hand, are designed to keep contaminants suspended, not to control temperature-dependent viscosity, so they’re not the same thing.