Blackstone Labs: 325i oil analysis at 65K miles
I bought this Arizona car, 06 325i, over a year ago with 59,000 miles. It had been dealer maintained, with I believe just the computer prescribed oil changes, the last one 10,000 miles before I bought it.
I had the indie shop that was now selling the car do an oil change, BMW 5w30. After 1,000 miles with 3 tanks of Techron to flush the fuel system, I changed out the oil for Mobil 1 0w40 (it idles smoother in the very high temps here.) That fill was in for 5,250 miles and this analysis is on it (stock oil and air filters.) I will follow Blackstone's recommendation and change at 7,000 miles. Next lab at 90,000 miles or as I get ready to sell it.
Pretty much confirms the conventional wisdom that 7,500 miles between changes is optimal for a NA (I did the same on my E46.)