'01 Silverado, 4.8, 250,000 miles, Castrol 10w30, changed by the computer. Peeking into the valve cover only a light brown tinting, no residue to be seen.
MHO... Except for cases of extreme abuse, a sludged up engine is a symptom, not a cause of failure. Once the compression rings are leaking, the engine will sludge up regardless how often the oil is changed or what brand of oil is used.