My 2020 Hyundai Sonata specs say to use 0W-20 oil. I recently had oil changed at dealer and they used 5W-20 oil. Some online sites say you can use either. What is the right weight oil to use?
Either is fine. 0W-20 is better for starting in very cold weather.
Whatever that’s mentioned on your oil cap/owner’s manual.
Check your owners manual. Some manufacturers have a graph showing the oil viscosities you can use depending on the ambient temperature.