Im not a super audi genious like some of these other guys, but everytime i get my oil changed i replace the filter. I think its to prevent oil contamination.
Change the filter every time. What good does it do to change the oil and leave a quart of dirty oil in the system. Also why try to save save $5 when your protecting an expensive motor?
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1997 A6 Avant 1998 Jetta 2007 Dodge Grand Caravan SXT one High Performance Roller Skate
i change my filter and oil at the same time. Even though Mobil ! recomends 5000 mile oilchanges with their synthethic filter and oil. I still do it at 3000, also if you want your motor to run better and cleaner, use the synthetic filters from mobil 1 i found they work the best :]
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30000km oil filters - 
