have heard discussions saying this is not just about miles to a oil change, but the government trying to reduce the amount of waste oil in this country.
Yes, it's true alright, according to a long article I read in an Auto Service Business trade magazine long ago. Here's the gist of it, as best as I can recall:
The government (EPA?) was concerned that literally tons of perfectly good oil was being discarded due to the standard recommendation of 3000 mile oil changes. The 3000 was intended to cover the worst-case scenario, to protect the engine (that was under warranty, of course). But, the vast majority of cars are NOT driven in worst-case conditions, so the 3000 mile rule was very wasteful for those cars. What to do?
The gubmint colluded with the smart folks at SAE, which resulted in the solution known as the computerized
Oil Life Index that's found in most cars today. The rest of the article then described and discussed those index algorithms. I had just acquired a car with such an index (2001 LeSabre) so I was very interested in learning about them.
The computer tracks four metrics to compute the index: RPM, oil temperature, time, and (I forget the 4th one; number of cold starts, maybe?). As driving progresses, these variables reduce the "percent of life remaining" in the oil, which gives differing results for each vehicle depending on its actual usage. (When I change my oil every 6000 miles, the Index generally shows 30 to 50 percent life still remaining. The manual says don't go over 7500 miles, or 1 year, as a maximum.)
Since there was no history with which to define the algorithms, three different "best guess" formulas were developed. Each one was then assigned to Ford, GM, and Chrysler for testing. As dealers did oil changes the oil was analyzed and statistics were compiled for SAE to evaluate the formulas, and eventually select the best one. And also to make improvements to it, if indicated.
So it wasn't just "gubmint meddling." Sounds like mighty smart business to me!