Had the AOS changed out 2000 miles / 6 months ago. Original replacement was because it would smoke on startup (the following day) if you drove the car hard and then gave it a nice cool down (with no boost in the last mile or so) and parked it left it overnight.

After the work got done I repeated this driving procedure several times with no issue in the first 5 months. All the sudden the issue came back and now you don't need to drive the car too hard as it would just do it with moderate boost, parking it overnight and starting again the following day.

Could this car have eaten up another AOS in such a short interval?

Had some friends who are mechanically inclined (they built an entire kit car in their garage level of skill) follow behind me and there is no smoke on WOT or anything like that, so I know its not blowing by the piston or something. Parked at the dealer and they are scratching their heads at then moment given they changed out the AOS 6 months ago. Boost is good, no warning lights, no loss of power. (991.2 C4S)

 

How many miles on your car? what model generation of 991? Turbo oil seals maybe. Does your intake plenum have oil all up in it?

 

What level do you keep the oil at? I've read that premature AOS failure can occur when the oil is overfilled. Other than that, I'd be guessing. Could have been a manufacturer defect on the new one possibly.

 

991.2, 2018 model year, built in late 2017. 26k miles, work was done at 24k miles February 2025. Not sure about the intake plenum.

 

Update: Dealer got the car to smoke on start up. (Not surprising) They have seen this a few times. They think the check valves in the turbo oil lines have gone bad and are overwhelming the seals in the turbos. There are 4 lines. 2 per turbo. What really sucks is 2 of those lines are an engine out service, the other 2 two are super easy to reach. They are going to try to with the two easy to reach lines and see if the problem persists or goes away. If it goes away then I am set. (At least until the other check valves fail)

Here is what it looks like at the moment.

Fidelity is not going to like me on Monday. Probably a good reminder to extend your warranty with Porsche or get some good after market coverage. If it gets to it, I cannot imagine an engine out is going to be cheap. If you don't address this quickly you can make your turbo's go boom. Were there any TSB's related to this?

 

Just for funsies double check you P/S turbo inlet pipe.... car that sit like to collect oil here and can get ingested by the turbos if there is enough. Also good to check the intake plenum in front of the TB as well, as it is also a good collection point for oil. These cars need to be driven more to avoid these type of issues.

 

Post 325 mile drive in one shot, I got it to smoke after it sat for 5 minutes.

 

FML its engine out. I cannot believe how stupid the porsche engineers were to integrate the check valves for the turbo oil lines into the oil line its self. They could have made it a separate part that's easily changeable, but nnnnnooooo they had to make it one part, which now failed and now requires and engine out to service/replace. Engine out for two check valves means you f'ed up as an engineer.

 

holy ish... hopefully Fidelity takes care of you and you get it sorted out either way.

 

I'm confused, Porsche changed your AOS 2,000 miles / 6 months ago? And now it needs to be replaced again? Second time around would be covered under the Porsche parts warranty.

Further confusion, each turbocharger has an inlet and outlet, OEM labor hours for both inlets is 3.8 hours and both outlets are 3.4 hours... 7.2 hours to replace all turbo oil lines on the (991.2) F6 3.0L Turbo motor... they want to drop the motor for one set of lines?

Trenton O. Gibson
tgibson@highline-autos.com
Highline Autos
Direct: 602.909.9216
Office: 480.348.0777

 

Its not the AOS this time, so they are replacing the turbo oil lines. The upper turbo oil lines are an engine out according to them.

 

I had this exact same problem on my 2017 C4S, I had the four oil lines replaced at a local indie and they were able to do it without dropping the motor.
I would suggest to check around and see what other shops can do for you, the dealership wanted to replace both turbos and the oil lines with the motor out and charge accordingly.

Mine has been about six months now and no more smoke.

 

Might not apply, but here's an interesting video that addresses the AOS.
23:48 - AOS overwhelmed, not broken
35:21 - aeration and foaming of oil
36:14 - higher end oil
For what it's worth, the quanity of oil found in my Vektor catch can has progressively gone down as I switched from Mobil 1, to Motul 8100 Excess, to now Motul 300V.

 

Update.... oil lines replaced, still smoking a little (not nearly as much) passenger side turbo seals have failed.... car has been down since September 3rd, cannot wait to see how long fidelity drags this out (waiting on them has been about 4 weeks of this process at this point) . Not sure when this nightmare is going to end.

 

It sounds like the dealer isn't sure exactly that is wrong with the vehicle... they're guessing at parts to replace, and when that doesn't work, they're going back to the warranty company for more parts to replace.

Trenton O. Gibson
tgibson@highline-autos.com
Highline Autos
Direct: 602.909.9216
Office: 480.348.0777