Question: what is the difference between 5w 40 and 5w 30 oil?
Answer: 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.