Join Date: Mar 2004
Location: Tulsa, OK, United States of America
When driven hard, the turbo gets extremely hot (hence the smoke) very quickly. If you turn it off without giving it time to cool down, the oil just sits in the turbo and cooks. This is what people mean when they say 'coking'. This is a primary reason for turbo failures.
On the other hand, if you drive around for a few minutes before shutting it down, the oil circulates through the turbo and cools it off. Since the oil circulates (instead of just sitting there), it doesn't cook.
Have a good day!
2003 Ford F150 Supercrew--------1996 Ford Mustang
Garrett 98mm turbocharger------12.10 @ 114 mph