I had my oil analized last week and just got the results back.
1999 E46 328i 28,000 miles on the odometer
11,000 miles since last oil change with BMW synthetic 5W40
(approx 50/50 highway/city)
The reports states that the oil still falls within the spec'ed viscosity range (5W40)
no trace of fuel, water, or antifreeze in oil.
and traces of metals (aluminum, iron, copper and about 4 other types of metal) were all virtually non-existant.
traces of silica (dirt) are also very minimal. (using K&N air filter) (there was a side note that said air filter is
The conclusion of the report was that the oil is suitable for continued use and engine is in excellent condition.
I think BMW engineers know what they're doing, and it'll be safe to go 15k to 18k before changing the oil.
When it hits 18k, I'll send the oil in to be analized again and will post the results.