Oil change intervals are based on block composition, head composition, oil filter quality, how often you drive your car, how many miles you drive your car, and how hard you drive your car.
The biggest problem in today's world is that people change their oil prematurely. If you really want to determine the correct oil change intervals, you can withdraw a sample size of oil and have it professionally analyzed to see the oil life remaining.
Changing full synthetic oil at 3500 mile intervals is stupid unless you rarely drive the car or drive the car extremely hard. Oil does have a shelf life, so don't expect to drive 1000 miles a year and change it every three years!
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