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Originally Posted by Destination: Moon
Whoa! Another contender enters the ring  ! Why would early changes promote wear?? These oils have so much chemistry that is for detergency and suspension that it seems illogical to get worse performance from changing early. How could that be? |
I'm an expert at maintenance, but alas my chemistry knowledge isn't sufficient enough to answer.
However, I can say the oil engineers at Caterpillar explained it all perfectly, so I'll see if I can find what they said an post it here.
What I do know is the wear metals in the oil analysis are consistently elevated on same engine/same oil (euro produced synthetics) when changed at lower mile intervals. These newer synthetics don't suffer break down until after sometimes 30k miles, with 20k miles being a very reasonable sweet spot between too early and too late.
IIRC, the way it was explained to me, the oil in the bottle (new) isn't the oil your engine really needs. It's only after an initial oil break in (who knows precisely how long that is, but it takes a little while) that the oil is conditioned to do what it does best. It's during that initial oil break-in (different from engine break-in) that you will find the engine wearing a bit. Longer intervals keep that oil break-in period from unnecessarily wearing the engine.
Hope this makes sense. By the way, the Castrol synthetic BMW is using isn't your father's Castrol - it's the latest generation of Euro spec'd long-interval diesel synthetic (after an initial break-in, it lasts and lasts and lasts)