Is it bad to mixing 5w20 with 10w30?

Mixing 5W-20 and 10W-30 motor oils is generally not recommended, as it can alter the oil's viscosity and performance characteristics. While both oils are compatible, combining them may reduce the benefits of the lower viscosity of 5W-20, potentially affecting engine protection, fuel efficiency, and performance. It's best to use the oil grade specified by your vehicle manufacturer for optimal results. If you must mix, ensure both oils are of the same type (e.g., conventional or synthetic) to minimize issues.