I'm on the diesel place forum. Lot of knowlege there, but a few misguided guys as well. Dont call anyone an "expert".
The purpose of cooling down a turbo is to make sure any trapped oil in the bearing dont cook. This can be detrimental to turbo life. I have a pre-turbo exhaust gas temp gauge on my Excursion. I will not shut off my engine with EGT's above 350 degrees. Even after the hardest pull, it only takes about a minute for the heat to decay. Usually, the creep thru my subdivision is enough to do it, and I dont have to wait at all.
the one thing you don't Don't DON'T want to do is rev the engine before shutting off the key. That will spool up up your turbo and it will coast down with no oil pressure. A neighbor had his new (to him) dodge for just over a year. Its got less than 60K miles on it and he already replaced the turbo once. He revs the snot outta anything he drives and shut the key off. You can hear his turbo winding down for a good while after he shuts it off.
My Exy has 188K miles on it, on the original turbo. You don't have to go nutso and idle it for 10 minutes every time you shut it off, but a minute of cooldown/spooldown goes a long way.
BTW, Idling a diesel is not harmful to it at all. even for extended times.
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