I just had my first oil change done on my new suv. I opted for M1 5W-30 as the price was really good, 31 bucks for 4.4 liters and the extra liter with it, not too bad in my books. I had the change done, when the shop super came and told me that Kia doesn't recommend sythetic oils? I asked him why, and he stated "I don't know. It may cause premature ring wear or something like that." I told him that my other car has ran the same oil since I bought it, and it runs perfect, M1 from the dealership. He said that cars do run smooter on synthetics. Is there any credence to this, or is he just trying to get me to pay 7 to 8 dollars per liter of bulk oil that he purchased for less than 1 per liter?
