What happens when you use 5w-20 instead of 5w-30?

Using 5W-20 oil instead of 5W-30 may result in reduced engine protection, especially in high-temperature conditions, as 5W-30 has a thicker viscosity at operating temperatures. This can lead to increased engine wear and potential overheating. However, if the vehicle manufacturer specifies 5W-20, using 5W-30 could also affect fuel efficiency and engine performance. Always refer to the owner's manual for the recommended oil viscosity for your specific vehicle.