5w40 motor oil is a synthetic oil that is thinner than 10w40 motor oil. This means it flows more easily at low temperatures, which is important for starting your car in cold weather. 10w40 motor oil is a conventional oil that is thicker than 5w40 motor oil. This means it provides more protection for your engine at high temperatures.
Mixing 5w40 and 10w40 motor oils can result in a blend that is not the correct viscosity for your engine. This can cause your engine to run less efficiently and may even damage it.
If you need to add oil to your engine, it is best to use the same type of oil that is already in your engine. If you are not sure what type of oil is in your engine, you can check your owner's manual.
