I have a lot of Pennzoil ultra 5w-30 syn motor oil. I know 0w-20 is recommended for this engine. Using thicker oil will reduce MPG also. Will it be OK to use this? I'm going to do my first oil change at 5K and have the dealer do it at 10K. I know syn oil can go for longer but I live in the city a good mix of highway and stop and go traffic. Should I do the first oil change sooner? I also picked up a 12 pack of cartridges from Toyota for $51.