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I wouldn't quiet say that's a good thing. Oil's job, along with lubrication, is to pickup dirt and sediments that can occur from the engine sitting, cold starting, or regular use. Thus if the oil is actually keeping that dirt, then it should get darker, if not that means it's getting scattered someplace over the engine.
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The Rotella has a very nice cleanup package. You won't have to worry about any sludge buildup with all the anti-soot additives that keep things clean.
The Rotella 5w40 is really really stout. After a 250 mile road trip, and 30 drag passes, it still held up for the drive home without losing viscosity and dropping oil pressure. Even the VR1 couldn't hold up to that.
For me it is the German castrol or the Rotella. Good stuff.
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