AOS replacement

I'm getting ready to replace the AOS on my 2010 Cayman. I'm looking at parts and see that Pelican and FCP both sell just that include all the hoses. Should I be replacing those at the same time? Thanks in advance.

Yes, replace it all in one trip. It’s also not a bad idea to put a magnet on the fasteners right before removal, a drop could be difficult to locate and the fastener isn’t going to be in your junk drawer.

Is this just preventative maintenance? I’ve heard that AOS is a non-problem on the .2s (and at almost 100k mi, seems true with mine… so far). Curious why you are changing it.

All signs point to it being failed. Some smoke on startup and vacuum on the crankcase. My engine stumbles or even dies when I remove the oil fill cap. I confirmed the pressure with a manometer. It was actually replaced when I bought the car at ~40k miles and it looks bad again at ~75k.

Do you run with the bars of oil reading at the highest line or one down? I run one bar open, might be worth a try.

Just be aware that the 987.2 runs significantly higher vacuum in the crankcase (by design) than the 987.1. So if you test with a manometer you need to make sure you're using the correct 987.2 spec, it's on the internet somewhere. The 987.2 OVS seems a lot more reliable than the 987.1 version and I'd be really surprised if it had failed that quickly. Yeah, I was getting a lot more oil into the intake (and more oil burn) before I started running one bar down. I still get some oil into the intake but that seems to be par for the course. To answer your original question: if your corrugated plastic oil vapor hoses are original they will be super brittle at this point and will crack if you breathe on them (ask me how I know this). So if you end up doing the job, yes, I'd replace those as well.

Knowing there has been some confusion on how to decipher the oil measurement digital readout, in the absence of a dipstick, just want to make sure there is an understanding of which is the ‘top line’. Reading from the bottom of the vertical bar, there are four lines. The fourth from the bottom is where the level should be. In the past I have seen some who believe the entire vertical bar should be filled, or white. If it is at the very top, it is overfilled. This image shows a correct level, at the fourth line. There should always be that thin black bar at the top. With the large volume of oil our engines capacity, one line down is not a major issue, though. Porsche officially states that oil consumption of up to 1 liter per 1,000 to 1,500 miles (approx. 0.8 to 1.6 quarts per 1,000 km) can be considered acceptable or within normal limits for a Boxster . However, a healthy, well-maintained engine often uses significantly less, usually averaging 1 liter every 3,000 to 5,000 miles during normal street driving . That seems like quite a bit of normal consumption. In my case, there is virtually zero consumption, as my level never wavers between oil changes. And for that, I am grateful.

Yep, but when I ran at the level shown in that pic I definitely got more oil into the intake (and occasional smoke on startup if the car was tilted funny) and higher oil consumption. I run one bar down from that now, which is about 0.25 qt. Engine has 90K, average oil consumption over the past 6 years (while doing the above) has been 1 qt per ~6000 miles, which is well within the "typical consumption" range.

Interesting. I'll have to find the spec and recheck. I do know that my engine stumbles severely when I remove the oil cap and I don't recall that happening previously. My fuel economy has also been suspiciously low lately.

I haven't cross-checked this yet, but this is what Claude is saying regarding vacuum levels: Nominal MA1: -15.0" H2O Healthy range: -14.0" to -16.0" Yours (1 psi): ≈ -27.7" H2O

Yes, -14 to -16 inH2O is the range that I look for with my 2009 987.2. I check my vacuum with a manometer once a year as part of my annual maintenance, when the car is fully warmed up and still running (after I've just come back from a drive), and it always falls right around that range... sometimes a bit stronger than -16.0 but I've never seen it more than -16.8. The car does certainly run rough and stumble with the oil fill cap removed. I have a new AOS sitting in a box, and I will probably replace mine proactively someday seeing as how it is more than 15 years old, but like others have said I don't believe AOS failure on the 987.2's is a big problem like it was on the 987.1's (the AOS components are different between the two), and my manometer readings are still falling within the normal range.

On our 2010 it was slightly smoky at startup. Changed the AOS , and yes, it was definitely starting to leak. Zero smoke since

My mechanic calls all those hoses "crack pipes" because they tend to age out and crack. So while you are in there, changing or replacing the AOS it would be prudent to change those hoses as well.

I just replaced the AOS first time, less than 1k miles later decided to spring for a Motorsports AOS and hoses. I had a shop do the second one, one of the hoses routed through tricky areas. Also, on the first OEM AOS , the bottom short rubber hose on the AOS is a PIA, watch some YouTube videos for tips on how to pre-set the hose clamp so all you have to do is move it in place after you get the hose positioned and release the clamp. Good luck, it’s a tight space to work in but the job is manageable if you take your time.

On the 986 Boxster S you needed to often change to the Cup AOS to control oil in the intake. Haven't seen much on this in years.

I just completed swapping out my old AOS for a new one. It's actually a very straightforward process on the 987.2, I think a lot of the reported difficulty must be from 987.1 models. Unfortunately, swapping out the AOS didn't help the situation; I'm actually measuring even more vacuum at the oil cap at around -61 inH2O. I went ahead and replaced the easy crankcase breather hose with no change. The second breather hose has a connection under the intake manifold that I couldn't reach without removing the manifold, so I held off on that for now. Does anyone have any other thoughts or recommendations? I'm considering a smoke test, but I don't think that a vacuum leak would result in a very high vacuum level in the crankcase. I have read that some AOSs are bad from the factory (I did buy a genuine Porsche part). The other cause I've read about is sludge, but I consistently run Mobile 1 with short oil change intervals so I doubt that would be the issue.

Years back when we had a AOS problem we change the Cup Car AOS which was difficult to install because it was so big but it was the only thing that worked.

I just performed a smoke test and didn't find any sign of leaks in the crankcase venting system. I'm still reading around 48" H2O of vacuum. I tried testing the old AOS using this procedurev documented on another forum ( plug two outlets, add light pressure to the third, and spray soapy water on the outside of the diaphragm portion) and didn't note any obvious leaks. I may try another AOS in case I got a dud and if that doesn't work, take it to a specialist.

Found this in a search if it is any assistance: An excessive or high buildup of vacuum in a Porsche Boxster crankcase is almost always caused by a failed Air/Oil Separator ( AOS ) with a ripped internal diaphragm. [ 1 ] Symptoms of Excess Crankcase Vacuum Stuck Oil Cap: With the engine running, it becomes very difficult to pull or unscrew the oil fill cap because of the strong suction pulling it down. Whistling or Hissing: A failing AOS diaphragm can create a distinct whistling sound from the engine bay. Excess Smoke: You might notice heavy smoke on startup as oil is pulled past the ripped diaphragm directly into the intake system. [ 1 , 2 ] Other Vacuum System Issues in the Boxster While a high-suction/excess vacuum state points directly to the AOS, the broader pneumatic system is prone to other common failures: Disconnected or Cracked Hoses: Small plastic vacuum lines (especially near the intake manifold, secondary air injection system, or behind the alternator) frequently crack or pop off, though these typically lose vacuum rather than increase it. [ 1 ] Faulty Change-Over Valves (COVs): Defective electro-pneumatic valves can misdirect vacuum signals to accessories like the exhaust flaps or coolant controls. [ 1 ]