You might be able to get away with using 10w30 oil in a 5w30 engine, but it's not recommended. The main difference between the two oils is their viscosity, or thickness. 5w30 oil is designed to flow more easily at lower temperatures than 10w30 oil. This means that it will reach all of the engine's moving parts more quickly when you first start up your car, and can help protect against wear. It also helps improve fuel economy since it doesn't have to work as hard to lubricate the engine. However, using a thicker oil like 10w30 in a 5w30 engine can cause some problems. The oil may not flow as easily and could lead to increased wear on engine parts. It can also make starting your car more difficult in cold weather. So while you might be able to get away with using 10w30 oil in a 5w30 engine, it's not something that we would recommend doing on a regular basis.