🔍 Key Concepts

• Definition of viscosity and how it changes with temperature and pressure • What cloud point and pour point actually measure in an oil • Effect of pressure vs. vacuum on fluid properties

💭 Think About

• Ask yourself which option represents a condition that directly changes how thick or resistant to flow the oil becomes, not just a temperature milestone or visual change. • Consider what happens to a hydraulic fluid when it is subjected to higher system loads versus when it is exposed to very low temperatures. • Think about whether cloud point and pour point describe properties at specific temperatures, or whether they are ongoing influences on viscosity across the operating range.

✅ Before You Answer

• Be clear on the definition of cloud point (appearance of wax crystals) vs pour point (lowest temperature at which oil will still flow). • Decide which of the four choices is a continuous physical condition that can directly increase viscosity during operation, rather than just a lab-measured property. • Verify which of the four is associated with increasing molecular resistance to flow under load.