the 4.8 is known for your symptoms when valve stem seals are bad. 4.4 smoke is more likely to be ccv problem especially in cold country. The most common course of action anywhere is a complete overhaul of the ccv system, using the cold weather version for locations like yours. That is because of how much damage a failed CCV system can do to the engine.

As mentioned, sometimes oil weight adjustments will reduce the smoke or even eliminate it for a period of time. The seals get brittle over time. I don't know of anything that will reverse that characteristic.

Since the oil is going into the combustion chamber your concern for downstream problems, not limited to but certainly including the cats, is justified.

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X5 4.6 2002 Black Sap, Black interior. 2013 X5M Melbourne Red, Bamboo interior
Dallas