Check out this article: WHEN TO CHANGE OIL

I know this subject has been beaten to death. However, there's the fact that millions of gallons of perfectly good oil are dumped every year and mega millions of $$ are wasted doing it. My Dodge Cummins recommends 7500 mile changes. That's a long ways from the old customary 3000 mile changes that many still use needlessly.

“In a time of deceit telling the truth is a revolutionary act.”
― George Orwell

It's not over when you lose. It's over when you quit.