Final answer:
Switching from 10W-30 to 5W-30 motor oil can improve fuel economy due to reduced friction at cold start-ups and efficient operation at normal temperatures, but the exact benefit varies based on vehicle specifics. This is unrelated to ethanol-blended fuels' effect on MPG.
Step-by-step explanation:
The question pertains to the fuel economy benefit of switching from 10W-30 to 5W-30 motor oil. The terms 10W-30 and 5W-30 refer to the viscosity of motor oil, which can impact the fuel efficiency of a vehicle. The 'W' stands for winter, indicating the oil's viscosity at cold temperatures, and the numbers before and after the 'W' represent the viscosity at cold and high operating temperatures, respectively.
It is generally understood that a lower viscosity oil, like 5W-30, can improve fuel economy because it reduces friction in the engine at cold start-ups and operates efficiently at normal engine temperatures. However, the exact percentage of fuel economy benefit from switching to 5W-30 from 10W-30 can vary based on vehicle type, driving conditions, and the engine's design. It's crucial to refer to the vehicle manufacturer's recommendations when selecting an oil viscosity for your car to ensure optimal performance and avoid potential engine damage.
While the use of ethanol-blended fuels such as E10, E15, or E85 can affect fuel economy due to ethanol's lower energy density compared to gasoline, this is a separate consideration from the characteristics of engine oils like 10W-30 and 5W-30. Flex-fuel vehicles are designed to operate on these ethanol-blended fuels but may experience a reduction in miles per gallon due to the differences in energy content.