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The oil change interval was born in the days of low miles per year, carburated engines and machining tolerances that are a far cry form today's engines.
The reason to change the oil is that combustion products will sneak past the piston rings causing carbon particles to build up in the oil along with acids that from from water and fractional hydrocarbons.
The carbon (remember diamonds are carbon) can score the machined surfaces accelerating wear and embedding to the point that the bearings are more like sandpaper than smooth, rolling, low friction surfaces. The acid can cause the same erosion of the surfaces.
So with all these products of normal operation of the engine being deposited in the oil the engineers set a point that the oil and filter should be changed. Then they took the average miles per year driven and divided the one into the other and came up with the figure that would get their engines through the warranty period with a very low failure rate. This worked out to 12,000 miles per year and four oil changes in that period. 3000/3 months.
The machining/materials have improved over the years to the point that some manufacturers are extending the interval to 15,000 or 1 change per year. In this time the additive package has improved in the oils as well.
I am a little old school and look at spending $100 per year to ensure my engine has fresh, clean oil to lubricate the moving parts cheap insurance. The vehicles I see with 200,000 + miles all have one thing in common, regular, frequent oil changes.
One other aspect is the people that are having one or two changes per year and use the quickie lube places never have a trained automotive tech look at their vehicle until it breaks and end up paying a lot more than $50 - $75 for the needed repairs that might have been spotted before they were left stranded with a large repair bill
Let me know what further questions you have about this
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