Turbo engine cooling - how long before I switch off?

I have recently acquired a Ford Fiesta with the EcoBoost turbo engine to add to our turbo BMW 535i. You have mentioned in the past about running turbos for a few minutes before switch off and I can't remember why. Does this still apply to these two cars and why?
After a long ascent and after towing. Though these turbos are water-cooled they can still get very hot and if they are switched off when very hot, the oil in the feed pipe to the bearing carbonises, eventually blocking the oil feed pipe.
Answered by Honest John on

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