ALLUC

Having been very diligently running the cool down period after running the car for long periods or where boost was used regularly I'm wondering if I couldn't just shut it down cuz:

My Drive home is 5 miles of little to no traffic but at a 35mph limit. It takes about 7 to 10 minutes from the freeway exit to my garage. I'm thinking since the car is not running hard for this last leg that this is enough of a cool down and could arguably be better since you still have airflow rather than sitting and idling

Is this sound thinking? My wife laughs every time she sees me sitting there idling.

rmc1148

That should be adequate for a cool down= opinions will vary lol.

Macster

The primary reason for the cool down is to cool the turbos. With the 996 Turbo these are cooled by oil and by air, mostly by air, and by "air" the exhaust from the engine. The exhaust temperature is the lowest when the engine is idling so that is why there is a 2 minute idle cool down call out in the owners manual.

The concern is if the engine is shut down too soon the heat in the turbos cooks the oil in the bearings and upon startup this cooked oil can degrade the bearings and seals.

Price a new pair of turbos and when your wife laughs at you while you are letting the engine idle and cool down tell her the price and ask her would she would be willing to do without to pay for the new turbos.

Dock

I'm never in enough hurry that I can't afford to sit for the 2 minute cool down.

wross996tt

There is a bimodal distribution of folks on this issue. Is your car stock? I have spoken with Kevin (I have his hybrid turbos) on this issue multiple times. My understanding is the turbos are oil cooled. When the car shuts down there is no oil running through the turbos, so they remain quite hot...I mean red hot. Now what the effect of this is I'm not sure since coking of synthetic oil may not be an issue. All I know is he told me to idle at least 60-90 seconds no matter what...even when you stop for gas...LOL Since he has had to rebuild many turbos, my guess is he knows what he's talking about.

rmc1148

Agree about the extra two minutes and I do it myself while opening garage door and other things on my return. It has been discussed many times and some of the more experienced people with these motors commented the best thing you could do is what original poster says he does= low speed no boost for the last few miles.

ALLUC

Yes a stock tune. I'll continue the cool down idle since it is easy and seems prudent. The irony is my wife's BMW F30 328 is also a twin turbo, but the BMW engineers set up a coolant pump and liquid cooled intercoolers...

rmc1148

It is easy and only takes a couple minutes= just ignore her giggling lol.

volv4life

Watercooled turbo's are a lot more resilient to this type of negligence.

Wealth Manager

Thats plenty of time for a cool down.........

Berra

If some of you don't have the time to sit for two min, why not put the car in neutral the last few meters? I do this, and the car cools down with airflow which is even better.

KNS

Actually they the term is "coking". A common issue with turbine engines and pretty much the same problem with automotive turbos. That's why a cool down is required for turbine engines before engine shutdown (I fly an AS350 helicopter that has a thirty second cool down, many Bell helicopters have a two minute cool down).

Some of the newest turbos (BMWs), as mentioned, are cooled down by the water circulated by the water pump.

volv4life

this is not new technology, volvo, saab, GM, and ford have all been using water cooled turbo's for 30 years now.

"02996ttx50

what I gleaned from that distinction was that the water cooled turbos don't require any cool down such as oil cooled turbos do. eg my 335i twin turbo didn't require any cool down.

cbracerx

Porsche put a water cooled turbo in the 951 (944 Turbo) back in 1986. In that car, the turbo was completely buried in the engine compartment with virtually no airflow, so it made sense.