Can I use API service SM, SL, SJ or SF engine oil on Kia optima 2006 2.0 16v engine
Any grade equal to or higher letter than specified in your owners manual. If the manual states SF all are fine.
Be sure to use the specified viscosity.
Only SM meets your car specs, and that’s only if it’s the correct grade and type:
Do you have a bunch of old oil sitting around?
17 years of use. Seems impressive for any car.