Yes, the oil life monitors (OLMs) use a fairly sophisticated algorithm to monitor the amount of wear on an oil from a variety of inputs including number of stops and starts, length of trips, total miles, maybe even ambient temps during the interval. Ahead of time they project what effect that will have on wear (they don't adjust for the type of oil you use, obviously) and try to get people to change their oil before a significant amount of damage is done.
I once saw a Civic owner that ran is oil until the minute the OLM said 0% ... he then changed the oil and sent the sample away for a UOA. The oil was completely shot and there were blatant signs of increased wear.
So, they are a tool ... and like a lot of tools in our everyday lives, they are dumbed down to the lowest common denominator. Following them is not necessarily the smartest way to go. Keep this in mind when looking at the OLM.
And no UOA I've ever seen is able to measure the coefficient of friction of oils. I've seen some manufacturer testing (I think it was from Red Line) and I was aghast at the drop across the board among all brands ... and the oils were not in use all that long.
Interesting about BMW using electrical properties. I'm not sure what conductivity oil has (I'm assumin it's poor) but it does make sense that as it accumulates moisture and acids, that value would change (increase) and that seems like a pretty good input as to the condition of the oil for an OLM.
Of course, I think that by this time the oil is well on its way to being shot so I'd want to change it before those properties change enough to register (of course I'm just guessing about the meter's sensitivity).
Because I travel about 9,000-10,000 miles per year and don't want to have to change my oil in the middle of winter, I end up changing my oil every 3,500 miles or so. Even if I went up to 15,000+ miles per year (which is what I used to do) I'd probably keep the same schedule.
For a lot of short trips (12-15 minute commute one way) that isn't too excessive and I diligently take my oil back for recycling, of course.
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--- Bror Jace
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