Question: what is the difference between engine oil 5w-30 and 5w-40?
Answer: Both of these motor oils are 5 grade when cold, however, 5w30 oil is 30 grade, and 5w40 oil is 40 grade at operating temperatures. 5w40 has a higher viscosity than 5w30 with higher temperatures in summer, which adds to the proper running of the car.