Generally, 5W-30 has better fluidity than 5W-40, which can reduce fuel consumption and quickly dissipate heat for the engine. For older cars, the noise of engine with 5W-30 oil is slightly higher than that of engine with 5W-40 oil. For engines that strictly require the use of 5W-40, if 5W-30 is used, it may consume more engine oil than normal, which is also commonly known as burning engine oil. At the extremely high temperature of the engine, 5W-40 has better oil stability than 5W-30. Car owners can choose according to their own car conditions.