Which component's design change contributes to improved fuel economy in Gen 5 engines?

The design change of the oil pressure control valve in Gen 5 engines significantly contributes to improved fuel economy. This component is responsible for regulating the oil pressure within the engine, which directly affects the engine's friction levels, efficiency, and overall performance.

By optimizing oil flow and pressure, the oil pressure control valve ensures that the engine operates under ideal lubrication conditions. This reduces unnecessary engine drag and friction, allowing the engine to run more efficiently and use less fuel. Furthermore, a well-regulated oil pressure can enhance the longevity of engine components and improve the engine's response during various operating conditions.

In contrast, the other components mentioned have different roles that do not directly influence the overall fuel economy to the same extent as the oil pressure control valve. For instance, while piston design and surge tanks play a role in combustion efficiency and engine operation, they don't primarily focus on optimizing oil flow and pressure, which are critical for reducing fuel consumption. The coolant sensor mainly monitors engine temperature and helps regulate the heating and cooling systems, but its impact on fuel economy is indirect compared to the function of the oil pressure control valve.