Its a matter of practice, not fact. If you are going to change the oil, you might as well change the filter too. Not because the filter is worn out, but because it has a litre of dirty oil in it.

If you are going to change the filter, you might as well change the oil, since you are in there anyway.

Both oil and filter are arguably good for 15,000 miles. Doing it early isn't bad, it is a feel-good issue, as we can't deny the positive reinforcement that comes from giving an engine clean oil and a clean filter. Wash the car at the same time, as it feels good as well.

In summary, if you are going to the trouble to change one, change both. If you want to analyze it, cut the filter open. It won't tell you much, except if it is full of particles, in which case you have accurate early indication of needing to rebuild your engine. The indication is free, however.

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2007 X3 3.0si, 6 MT, Premium, White

Retired:
2008 535i, 6 MT, M Sport, Premium, Space Grey
2003 X5 3.0 Steptronic, Premium, Titanium Silver
2002 325xi 5 MT, Steel Grey
2004 Z4 3.0 Premium, Sport, SMG, Maldives Blue