Here is a graph of oil run to 18k miles.. shows ppm per mile starting to level off at 3k
Ofcourse makeup oil probably skewed the data but still 5k seems palatable.
Full read
http://neptune.spacebears.com/cars/stories/mobil1.html
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Interpreting Wear Metals
Looking at a single oil sample's wear metals wouldn't impart much useful information. Frozen in time, with no trend to compare it to, it would serve solely as a pass or fail mechanism: either the wear metals are excessively high or they're not. While that's useful to know, it's only part of the story. The rate of accumulation is actually the more useful measure, as it allows us to see whether the oil's protective ability is improving or weakening. Iron, copper, and lead are the three most important wear metals, as they derive from the components most prone to wear, such as piston rings and various bearings.
The solid lines are the standardized cumulative totals of wear metals in parts per million for iron, copper, and lead. The shaded lines are the standardized totals of wear metals in ppm per mile -- in other words, the shaded lines represent how quickly the wear metals accumulate as compared to how quickly the miles accumulate.
While the wear metals all accumulated steadily over the course of the test, the highest concentrations of accumulation per mile occurred in the first 3,000 miles of the test! From the 3,000-mile mark all the way to 18,000 miles, only lead showed an increase in per-mile wear beyond 3,000 miles. Yet even with an increased wear rate, lead wore the least in terms of absolute wear. For iron and copper, the longer the oil remained in service, the lower the wear rate got.
In case it isn't obvious yet, this means that the most wear occurs in the first 3,000 miles.
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