hey guys my g/f got a `04 G35 coupe last october for her first car/18th bday present (yea not so bad huh?) well anyway i did the 1k oil change with castrol gtx 10w30, then the next oil change at 3k with valvoline 10w30 and just yesterday a 6k oil change with mobil 1 10w30, i figured by 6k miles the engine should properly be broken in enough for synthetic. the car has the VQ35 (3.5 V6) engine the nissan/infiniti uses in lots of their vehicles and i was wondering if 10w30 from mobil 1 is a proper weight to be using. the car lives in so.cal so it had mild temp. year around and a fair amount of city driving (make that mostly city driving) would 5k intervals of oil changes with mobil 1 be safe also? thanks for any help.