what is the difference between 5w 40 and 5w 30 oil?
This term is defined as how well the liquid will flow through the engine. The working viscosity of 5w30 is basically from 9.3 to 12.5mm2/s whereas the operating viscosity of 5w40 is 12.5 to 16.3mm2/s. That means 5w40 has larger viscosity than 5w30. So, 5w30 is better than 5w40.