Manual/Manufacturers specify whatever intervals, but does the oil really last that long? When does it actually break down? Conventional is rated at 3k and most synthetics are at 6k, rated for normal driving conditions. In the end it does not matter what anyone says, you just do what you feel is right for your vehicle.

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Sasakyan Kita
'96 E36 / '02 E53 Sold / '07 E70