Which is quieter between 5W30 and 5W40?

[SanLukas]

5W40 tends to be noisier than 5W30. The number after the 'W' represents the kinematic viscosity of the oil at 100 degrees Celsius. A higher number indicates higher viscosity, which means better protection at high temperatures. It can also be understood as representing the oil's stability at high temperatures (i.e., its resistance to thinning). The larger the number, the better the oil's high-temperature stability. Thicker oil makes the engine work harder, resulting in louder noise. In practice, the choice isn't solely determined by the oil grade, as it also depends on factors such as the vehicle's class, age, and driving conditions. Additionally, using an inappropriate oil grade can lead to excessive engine noise. Therefore, it's essential to follow the vehicle's owner's manual for the correct oil grade. The main difference between 5W30 and 5W40 is their viscosity. 'W' stands for winter, and the smaller the number before the 'W,' the better the low-temperature fluidity and the lower the applicable minimum temperature. The number after the 'W' indicates the oil's kinematic viscosity at 100 degrees Celsius. A higher number means higher oil viscosity, so 5W-30 oil has slightly lower viscosity than 5W-40.