What kind of oil does the 2005 Kia Optima use?

The kind of oil the 2005 Kia Optima uses iS5w-20. Your oil needs to be changed out someday. Every 5,000 to 10,000 miles or so is a good rule of thumb. If You don't replace it, there will be problems with the engine. Having high quality oil is essential for the engine to run smoothly. You will run into problems with the oil at some point. A common problem is an awful burning odor. This needs to be viewed closely as soon as possible or the car might explode. Old or bad oil can cause the engine to stop working. Knocking noise may arise from the engine. You could experience poor gas mileage.