I got this from another forum that I am a member of and the source is Infamous Performance and Tuning out of CA. Who source it from a Master Subaru Technician and is a copy paste from an internal memo. That being said I am sharing for feedback and pretty sure it only applies to stock configurations. Subaru Turbo Cool Down Procedure It is not necessary to perform a “cool down/idling” procedure on Subaru WRX/STi/LGT turbo models, as was recommended with past turbo models. The current 2.0/2.5 liter turbo engine has a far greater cooling capacity and, coupled with technology advances, makes this practice no longer necessary. This explains why information about a cool down is not included in the Owner’s Manuals. The heat contained in the turbocharger begins to vaporize the coolant at the turbocharger after the engine is stopped. This hot vapor then enters the coolant reservoir tank, which is the highest point of the coolant system. At the same time the vapor exits the turbocharger, coolant supplied from the right bank cylinder head flows into the turbo. This action reduces the turbocharger temperature. This process will continue until the vaporizing action in the turbocharger has stopped or cooled down.
This is accurate. For example, the stock turbos on my 911 aren't water cooled (just oil cooled), so the owners manual suggests letting it idle for 2 minutes after every drive. Failing to do so results in some smoke on start-up from the coked oil. Not the end of the world, but something that comes up constantly in forums "zomg my kar iz smoking. Did it died?"
To me there is a big difference between cool down and spin down. Subaru has always done a good job of using water cooled turbos and convection to cool the turbo housing after shut down. That cooling doesn't release you from good shutdown procedures. Modern oil also does a better job on NOT breaking down under extreme heat and pressure. Bottom line: Don't shut your engine off right after zooming the turbo.
