As John pointed out the cooler has a bypass thermostat that opens at 95C or around 200F and below that it completly bypasses the cooler stage so the oil can at least get warm enough to drive the moisture out, during the winter it would not be very good to have the oil running at say 50F all the time being cooled by cold air and the net result would be lots of sludge.
Your switch to mobile-1 is a good move in itself so I wouldnt worry about it at all.

The whoosh sounds like a leak on the pressure side or maybe the wastegate is frozen up in the open position however I doubt that. Look to see if any of the couplings between the pipes has broken loose, it doesn't take much of a leak to drop the boost way down.

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