Originally Posted by engineerboy

do a search for "oil test" or somethign like that... there's a long term study that's being done by this guy who drives his corvette pretty hard. He's been testing the oil every month or 1000 miles (which ever comes first) to see how much cleaning and lubricating power it has left. He has to change the filters but basically, the lab tests are showing that Mobil 1 synthetic and Royla purple (I think) both have effective lives above 18000 miles.

The change your oil at 3K story is a myth perpetuated by the oil industry and they've even admitted it. In the late 70's or early 80's documents were "released" showing that industry leaders were trying to make as much money as they could- and motor oil has a decent profit margin. Their own tests showed that oil was effective for lubrication and removing deposits into the 7000 mile range.
how often do I change my oil? Every head swap or 4500 miles- whichever comes first