When do I change the oil?

The 3000 mile oil change was important in the 70's, when engines were far less efficient, and oils were closer to crude. Modern engines are designed with closer tolerances, and far less blow by, so the oils are absorbing less crud as the engine runs. The oils are also made far better then 30 years ago. The people that designed the engines know far more about their engines then most people typing on the internet, so in almost all cases you are better off going with their recommendations. For most of us all you are doing by 3k oil changes is spending more money then you need to, and causing more waste oil and filters to be processed then actually needed. If you want to get some stupid long oil life, get secondary oil filtration, run a good synthetic oil, and get analysis every 3k until you know how long it lasts, then go to 50%, 75% and 90% on the analysis. Some people are getting upwards of 50k on the oil, only changing the filters and adding make up oil (for what is consumed in the engine and lost in the filter changes).