Quote Originally Posted by osbornk View Post
I agree. I don't change oil because it is worn out, I change it because it gets dirty. I don't think it makes much difference what the dirt is floating around in. Like someone said long ago here regarding oil "any oil is better than no oil and clean oil is better than dirty oil".
Actually in the 21st century some of this is no longer true.

Once the cleaning additives have done their job and suspended whatever "dirt" there was, the oil itself becomes a better lubricant. Constantly changing the oil at shorter-than-recommended intervals means you've always got poorer lubricating oil in there.

This of course applies to the synthetics designed for long intervals and not for ancient formula (but ultimately more expensive) dino oils.

http://papers.sae.org/2007-01-4133/