Oil life?? Time vs. mileage ....

That's a good question. The oil companies would have you believe 3,000 miles or 3 months. Personally I believe you could double those numbers, as long as you have a good filter, don't overheat the car, etc.

20/20 tv series did an episode on this very thing, using NewYork taxicabs as the control group; over a period of a year. They found NO measure able difference in 3,000 mile oil changes vs 7,000 mile intervals