I agree with Boosty that your driving styles dictate your oil-changing frequency. If you do short commutes, like city driving, the oil will deterorate faster.

For my oil changes, I go by the color of the oil. When it starts to get a deep-brown color, out she comes.

please, get your oil analyzed, then you can make an informed decision on if your oil is clean or not at a set mileage@3k, 5k, 10k.
i have changed my oil 16 times in 145,000 miles, with 3 GAS ENGINE OIL ANALYSIS
that said i could have gone further but at every 10k its easy to remember when to
change the oil. i get my oil analyzed at http://www.blackstone-labs.com/index.html
it also tells you if your air and oil filters are doing a good job?

ROD

That'* what I do too in my diesel. Except I run the full 15k on one filter and change, or I'm trying to I should say. I'm going to get to 10K and do an oil analysis. Which you can also get the kis postage paid through AMSOIL for like $20 and then you send everything off to http://www.oaitesting.com for analysis. Check'em out here:

https://www.amsoil.com/storefront/oai.aspx?=zo1475014

Let me know if you wanna get hook'd up on AMSOIL. Check out the links in my sig for free catalog and the amsoil store