Corso

Question for Turbo owners......

As most are probably aware, it is known that a good customary practice for turbo cars is to allow the turbo(s) to cool by letting the vehicle idle a minuet or so before shutting it down. More so after hard driving. I have a buddy with a couple turbo cars (non-Porsche) who does this religiously out of habit.

As I understand it, it seems the Cayenne has been engineered to allow for better-than-adequate turbo cooling. With that said, is the aforementioned practice unnecessary? Do any of you still do this? Thoughts, comments, advice?

Thanks.

Jochy

If the owners manual doesn't mention such practice, German engineers took care of such practice already in your 95x design

porschefan931

The 955 has water cooled turbo's not sure about the 957 onwards but i think the same. There is a thermostat that will circulate the coolant to the turbo's.

I used to own a 924 Turbo and would leave that ticking over for a minute or 2, i think they only brought the turbo cooling in on the 944.

DWPC

Idling for a bit before shutoff is an old school practice from the early days of turbos on car engines when oil could bake ("coke") in the turbo oil passages of hot turbos and block them. Turbochargers on CTTs are water-cooled and (I'm pretty sure) have an electric aux coolant pump that continues circulation after engine shutoff if the oil temp is high. But I still let it idle before shutoff as a habit after many years of an '84 MB 300D turbo diesel.

cwazyeurodrivr

after any type of driving hard, casual, daily driving whatever. I always let it idle for 90 seconds or so while I gather my phone, coat, laptop bag etc. Just to let everything settle down and let fluids flow not under load and cool down a bit.

AGARubberDuck

The manual (for 955) specifically states to not let the car sit idling (granted, it really only specifies on start up). Pretty sure this is the reason they do not come with remote start. As others have said, they are water-cooled. After really tearing it up and then shutting it off, you'll hear a motor going for a few minutes when you leave.

hahnmgh63

I also let it idle for up to a minute of driving hard. If for nothing else a little cooling of the Turbine housing and to let the Turbos spool to their idle speed. Yes the bearing are water cooled but I'm old fashioned. The N. America manual say's not to let it idle, and also say's not to let it warm up but to drive right off but drive easy. I think that is more of an EPA mandated thing otherwise the EPA would make them do it in their Cold start emissions cycle, funny the German manual doesn't say that? So yes, if it's cold I'll usually let it idle until the SAI fans stop running, that is the same time the idle goes from high idle to normal idle.

user 83838290

Do it, idle at least for a minute.
Take a look at how the oil and water lines are run around turbos. I wrapped mine in heat resistant stuff - they are right under the headers, especially oil lines. I also cut open my hood to reduce temps.

My friends' 09 CTTS blew a turbo just because of carbonated oil in one of those lines.

cwazyeurodrivr

How much of a pain in the lower backside was it to wrap both turbo supply lines with heat or ceramic tape/wrap ?

wrinkledpants

Not necessary. The Cayenne has an after run cooling system. When you hear the fans running after shutdown, there electric coolant pump that also runs and circulates coolant around the turbos to keep any heat soak from coking inside the bearing housing. It uses the amount of time spent in load, as well as coolant temp to calculate how long to run the after run cooling system. The Cayenne has an immense amount of cooling power given that it's 450 HP out of a 4.5 liter motor, and can tow 7700 lbs. Very few turbo failures, oil temp rarely moves, and it's a ball bearing turbo - it's an incredibly robust design.

Unless you're on a track, just towed a heavy load up a long mountain road, or spent an appreciable amount of time in boost (aggressive driving up a long mountain road) - it's unnecessary to let the car idle.

wrinkledpants

They spec not to let the car idle when cold because you extend the amount of time spent in the highest wear condition - engine cold with no load. The air injection pumps and open loop fueling maps do a pretty descent job of keeping the emissions down while the car gets up to temp.

It only takes 10-15 seconds tops for the turbo to spin down from 100% to idle rotation speeds. Even if you tried, I'm not sure you could go WOT, smash the brakes, slam it into park, and shut it off before the turbo was fully spun down. Even an F16 will spin down from military power to idle in 10 seconds or less. And, it has far more rotating inertia than the tiny 955 turbo.

user 83838290

You are right and wrong at the same time. The problem is not the water circulating. I know it does circulate after you shut down the engine and believe me, it runs for 8min on mine when I come home after an hour of doing 160+mph - and that's after I get into urban area doing 30mph for 5min.
The problem is, as I described above, that the oil feed lines to turbos run right next to headers and the turbo itself (which can glow orange from being hot, maybe got a pic of that as well). I've seen what was inside of that pipe, it was not possible to blow through it with a high pressure compressor at all, guys had to clean it with a steel wire and decarb it with lots of chemicals.

I'll look for the pics on my computer when I get home. You'll see what I mean.

As for doing it - it's nearly impossible to do without removing exhaust including DPs and dropping the front axle.

wrinkledpants

Your post about a clogged feed line is probably the first time I've ever read about that actually happening and causing a turbo failure in an Audi/Porsche. I don't see how that's actually possible unless you're running the wrong oil, or have really poor driving habits. The radiant heat a feed line gets is substantially less than the inductive heating the oil gets being in contact with the turbo. Not only that, the time that oil spends sitting inside the bearing cavity will be longer than the time oil spends in the feed line.

If that was a major problem, you'd hear about a lot of people with clogged feed lines. I've only read about 2, maybe 3 actual turbo failures. I've seen a lot of maintenance records in a CTT showing a turbo replacement early on, but it was almost exclusively the driver side, and the reason was oil in the charge pipe. Porsche caught on to this, and it's the reason the TSB was issued that oil in the charge pipes is normal, and not likely evidence of a turbo failure.

Extenuating circumstances might warrant 30 seconds, or so, of a cool down, but certainly not for daily driving, or even aggressive street driving.

Corso

A lot of great theories and ideologies behind why it may be (or may not be) a good idea, or completely unnecessary. I'm glad I asked. This car is unchartered waters for me so I am just trying to educate myself as best I can.

Thanks, gents. Please continue.......

user 83838290

here are the lines. the one right under the headers is oil. unfortunately, I don't have the pic of the pipe itself. said car was always run on 0w-40 mobil 1.