If you are really concerned about your oil, and the determination factor of when to change it, do an oil change, at the end of the 3000 miles send it HERE they will do 4 tests on your oil, including if your oil has started to breakdown. After using them for 1 year, I now only change my oil 4 times a year and use a K&N oil filter. The number one reason is because I use fully synthetic Mobil 1. Synthetic oil doesn't break down in the same manner as conventional oil. Unles of course you encounter a High heat situation. Such as an overheat. But either way, if you overheat your engine or even come close, you really should change your oil anyways. For example, I will change my oil on the first day of Winter, first day of Spring, Summer, and Fall. I started to notice that when I changed my oil only twice a year there was a very very small amount of water in it. Now that I change every season, there hasn't been any water in it at all.

Here is another thread that has been ongoing for awhile.
Good link as well.

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