This is one of those subjects that gets far more discussion than it probably deserves. Most everyone agrees that 15,000-mile oil change intervals are not in the best interests of the car if real longevity is a concern (150,000 miles and up). Beyond that, the debates begin. So in the interest of reducing worry by owners of new or still-young Bimmers, I thought everyone might like to see what the inside of a high-mileage, well-maintained engine looks like. These are photos of the valvetrain of an M54B25 engine in a 2001 325xi. The oil and filter have been changed approximately every 7500 miles since the car was new. The only oils ever used are Mobil1 5W30 and BMW High Performance Synthetic 5W30. Filters are OE BMW parts. The car is driven ~50 miles per day, mostly highway commuting miles, for pretty much every week of its life except when I was on non-driving vacations. This engine is just over 210,000 miles old. It pulls strongly, smoothly and easily to redline and in terms of power and torque feels pretty much the same as just after break-in. It sees 5000+ RPM shifts every day and redline--just shy of the rev limiter--pretty much weekly. It has never been abused but never been babied, either. Oil loss is about 1 quart per 3000 miles. The catalytic converters are original and the car has never failed an emissions check. Please excuse the large dimensions but these are quick, poorly-lit cell-phone shots that will not resize well. This is the VANOS unit and cylinders 1-3. There is some light buildup in the corners of the VANOS housing where oil cannot easily drain away, but nowhere else. This is cylinders 3-6. Note the complete absence of sludge or buildup of any kind. The light gold varnish on non-moving parts is soft enough to be rubbed off with a shop rag. (I tried, in a small spot not in the photo. Calling it "varnish" is almost an exaggeration.) If you look closely at the forward exhaust cam lobe on cylinder #3 (bottom right of this picture) you will see a small variation in the finish--a shinier stripe at the forward edge--which is pretty much the only sign of wear on the cam. The variation is undetectable to the touch, even with a fingernail. I don't regret being unable to provide pictures of the bottom end of the engine. However, I replaced the oil level sensor a few thousand miles ago and found pretty much the same conditions inside the pan. (The tiny bit of it I could see/reach anyway.) These photos are unretouched and the only cleanup I did was to wipe down the gasket sealing surfaces. Other than that, what you see is what I've got. Modern synthetic oils are truly very, very good at keeping an engine clean and resistant to wear. This is perhaps THE classic "your mileage may vary" issue but I hope these photos and description of the engine's history help you decide how to care for yours.