I change it when it doesn't feel like lube anymore. Hard to tell exactly how many miles that is, but that's when I do it.
Filters actually get better with age. That is to say that the older they get, the smaller the pores in the filter media get, and the smaller particulate can be filtered by it. Extrapolating from that, you can probably come to the thought that premature oil/filter changes are WORSE for your engine than waiting for 10-15k...
The bypass valve in an oil filter doesn't work based on your oil pressure... it works based on pressure
differential. That is to say: When input pressure and output pressure are different by X (spring rate, in lbs), the bypass valve opens. It has nothing to do with the filter being plugged, etc... it usually happens when your oil is very cold or extremely thick.
Given the additive packages present even in dino oils these days, it's NEVER prudent to change your oil at 3k... most of the additives haven't even
activated yet, let alone worn out.
Color is
not an indicator of when to change your oil. Black doesn't mean it's dirty, or burnt.
You can gauge your oil pretty well with your fingers... rub it between them. If it doesn't feel like it's lubricating, there's a good chance that it's not. If it feels nice and slick, with no grit in it, then it's most likely fine.
That's my $0.02, take it or leave it.
