1AS

I think the "drive right off after starting" rec is due to the rich condition washing oil off the cylinder walls. The result of rich idling may be counter-intuitive to "warmer-uppers".
One last thought on cool down. If my 30 minute highway drive is followed by 1.5 miles of surface traffic with 4 stoplights, why doesn't my last stoplight count as cooldown? How much turbo heat do I really build up in the last block of 25 mph before I park? That is almost idle in second gear. My point is that routine drivng is unlike "hard" driving. The normal breaks seem sufficient to allow a return to cooler temps. AS

Kevin

The combustion process is to good to have raw fuel burning the cats up. The O2 sensors do a good job on the idle circuit. Yes, it is rich but not like running carbs and dumping raw fuel in excess.

Rad22

I once owned a SAAB Turbo SPG (1985) with rather non-ambiguous owner's manual instructions about the cool-down after any driving. I recall an aftermarket company once sold an "oil accumulator" which was nothing more than a cannister plumbed into the oil circuit. mounted at a higher level than the turbo in the engine compartment, that accumulated about a pint of oil while the engine was running, and then allowed it to flow through the turbo bearing by gravity for the few minutes after you shut down the motor.

Never had one installed, but it seemed like a good idea. Wonder why Porsche and others haven't pursued such a solution if the bearings are at such risk after shutdown. The old SAAB manual said that, at shutdown, the turbine is still spinning at high speed and will continue to spin for a short period after shutdown. The fear was that if it was spinning at a very high speed, you may inadvertently shut down the oil supply while it is still spinning, thus supporting the notion that this accumulator may be a solution.

Kevin

Rad, the problem with that approach is that our turbochargers are placed below the centerline of the crankshaft. We are battling oil levels in the sumps. We actually have a sump pump that is located on the front of the intermediate shaft that sucks the oil out of the sump tanks on each side of the engine. Flushing oil into the turbochargers after the engine is shut off will flood the level of the sealing rings and oil will migrate into the compressor housings and turbine housings.

Rad22

Thanks for the explanation, Kevin. Makes sense.