I think it’s possible that I never dump out old oil completely. The pan drain being 1/4" above the bottom of the pan on my car, I’d have to be in a steep incline.

I know from doing trans flush that the sediment and thicker stuff will aggregate in the bottom, sort of making a film.

Is engine oil the same way? Is Oil draining back down slow enough to layer like a fancy cocktail? Will the pan accumulate some thicker slurry of oldest oils in the bottom over time?

Or is all new and old oil somehow agitated and mixed in the very bottom there?