OK, I did a search here and could not get a definite answer to this question. I dumped the factory fill today at 1026 miles and put in Pennzoil Synthetic 10W30 (for summer) with a Purolator Premium Plus filter. I wanted to use synthetic because the car only holds 3.6 qt. with a filter change and wanted to help against thermal breakdown and heat control with such a small amount of oil. Car in question is a '04 Kia Rio. Am I correct in assuming it was OK to put in synthetic at this point? I read here most of the break-in occurs in the first 1000 miles. The car seems to run smoother. Also, I think I remember reading the Pennzoil Synthetic was not a true synthetic?? Another question...is a Group III oil OK to use?? Thanks for your patience...so many questions.