If an engine lubricating oil's viscosity is given as 20W-50, what does this mean?

Correct Answer: Option A — The oil is formulated to meet the low temperature requirements of SAE 20W oil and the 100C (high) temperature requirements of SAE 50 oil and as such is a year-round oil.

Multi-grade oils like 20W-50 use viscosity index improvers to maintain performance across a wide temperature range. The 'W' denotes winter/low-temperature pumpability, while the second number indicates the viscosity at 100°C. This formulation allows the oil to provide adequate protection during cold starts and high-temperature operation, making it suitable for year-round use.