So I just had an oil change about a week ago. Paid about $40 for the change, regular oil. I happened to pass by my local autozone after the oil change and saw that 5 quarts of 5w-30 synthetic oil costs about $30 and 5w-30 regular oil is about $16, total rip off. After that I figured out how to do oil changes on my own. Question is, Can I just go ahead and buy and use the synthetic oil? Will that mess up my engine?