Q: Oil for my car 2005 Hyundai Accent

Hello - not ideal perhaps, but yes, you can use the 5W30 oil in your engine. Since we are in the winter months, the lower "viscosity" rating (5), is more important - measuring the fluidity of the oil at lower temperatures. There may be an imperceptible decrease in fuel mileage from the slightly increased resistance of the oil at higher temperatures, but it won’t be much.

You should not use the thicker oil. The recommended oil is the proper viscosity for the proper lubrication of the motor as it was designed. Using the thicker oil may damage engine components from lack of oil lube getting to the parts as needed.