The turbocharger has both coolant and oil lines running through it. I think the turbo idle time is valid if youve been towing or running it hard, but for daily driving around town youre fine.
As stated above we have both coolant and oil going through the turbo charger. The coolant does the main cooling itself and the oil really just keeps things lubricated before things go Haywire. If you have been running it hard which is most likely since we have turbocharged vehicles and or have been telling it is definitely recommended to let it idle for about a minute before shutting off. Mind you I already have close to forty seven thousand miles on my truck and I have yet to have an issue. Also for Extra Protection it wouldn't be a bad idea to run full synthetic oil in the truck as extra preventive maintenance.
You can always get a turbo timer. Not sure if anyone has gone this route before. Basically it lets you turn your ignition off and walk away with the key, but the vehicle stays on for a set amount of time to allow cooler, then turns off.
The problem comes in running up. Getting that 30,000 rpm shaft and bearing boiling hot then shut it off. The oil can bake into a carbon rock. That will tear the seals out at the bearing and you’ll start turbocharging oil into the intake. Saw it several dozen times back in the 90s. Not so much now.
The water cooling is more to control the temperature spike when you shut the engine down. Cooling a turbo Prior to shut down is not that necessary now. I still would not go from high power to off in less than 5 min or so. Driving normal at highway speeds or less no cool down needed.