996 Air Oil Separator

Recently the car started to produce a tremendous quantity of smoke from the exhausts. From googling it seemed obvious that it was the Air Oil Separator which had failed. I came across a few useful videos and guides for the AOS replacement which I thought I would share here for future reference. https://www.pelicanparts.com/techar...Oil_Separator/09-ENGINE-Air_Oil_Separator.htm https://rennlist.com/forums/996-forum/595923-so-i-replaced-my-air-oil-separator-2.html I watched and read how to do it, then did it. It is a really tight and fiddly job to do with the engine in the car and without a car lift but it can be done. I used an OEM part 99610702355 for £118 from Porsche Nottingham. Most of the articles suggest that you need to lower the engine from its mounts a touch to gain access and that you need to remove the coolant tank. I found that these steps were not necessary. Our car is probably the tightest and fiddliest model since it is a 3,4 Tiptronic , but provided you've got the correct tools and plenty of patience you can do it. My tips are: Pressure wash thoroughly inside the rear left wheel area where you will be working. Our AOS was partially hidden under mud. You can undo the air inlet manifold bolts from the inside (i.e. by going into the area that is exposed when you remove the alternator) by using a very small 1/4" ratchet and 10mm socket. A tricky part is unclipping and re-clipping the lower air/oil pipe on the AOS, but I realised that once you have unbolted the AOS from the engine block, you can pull the AOS up high enough to get to that pipe connection from inside the engine compartment (rather than trying to do it from below the car as they do on the FCP video). My biggest tip however is, for goodness sake, do NOT try to re-use the hose clamps from old AOS like I foolishly did - they leaked. Afterwards the car still smoked quite a bit for a couple of days as the oil left inside the manifolds was sucked through. Now I'm hoping the cats are still working OK for its upcoming MOT.

nice write up @Carrera4Boy'sDad The AOS is basically a small diaphragm distillery which distills the minute amounts of oil mist in the crankcase, liquifies it and sends it back to the crankcase. The "clean" air is now sent into the air intake (after the throttle body) to be burned off by the engine. When the AOS starts to fail it cannot separate all of the oil out of the mist and some liquid oil is sent to the air intake. A few drops of oil is enough to generate the GREAT SMOKE BOMB for which our cars are famous for. A big smoke bomb once in a while is completely normal, due to the architecture of the flat-6 engine, which may let a drop of oil flow into one of the combustion chambers sporadically.

Hi does anyone have any ideas where this bellow pipe actually goes as I cannot see any where was just advised to change whilst replacing the AOS thanks

On the pipe directly above as far as I know

When I took the old AOS off that didn’t come off with it and seems to just go straight into the block.

Maybe there's 2 types. I know my 99 Boxster had the bellows and so does my 98 996 3.4.

Yes I think your correct mines a gen 2 and believe it doesn’t use this part. Thanks

Word of advice: Don't cheap out on the AOS itself! I had mine replaced when my engine was rebuilt and the part that eventually arrived was an aftermarket "Hamburg" or something brand. I then had to replace it again after about 10k km as it was letting oil through. Only use OE parts for this.

Thanks for this yes I got the part direct from Porsche and wasn’t that much more expensive. Thanks

I replaced mine with a Porsche part when I was having a few other things done after buying the car as a preventative measure. There's a guy on Rennlist.com that's created the UAOS (Ultimate AOS) that's designed to never fail. If I were to do it again I'd puy one of those from the US and completely futureproof the car. Its also better if you track the car as that puts additional strain on the AOS.

Yes, I wholly recommend the UAOS, too. I have it installed along with the optional “Track Drain” kit, which drains the oil from the accumulator back into the sump. With the UAOS, I overfilled my engine oil by a full quart without a single worry. The OE style AOS risks hydrolocking unless you keep the engine oil level a half-quart below the maximum level. The UAOS also eliminates the coolant ports at the separator, removing a possible source of oil & coolant intermixing.

Anyone got any fitting tips? I whipped the old one out quite easily but I can't get the new one into the block, even after a combined 2.5hrs of pushing, prodding and wiggling. I get the first 1~2mm in but no further.

Is it a genuine part?

OE Match from Design 911

I'm just in process of replacing the bellows as it was leaking oil. Also swopping out the Cam sensor while I'm there. I was going to change the AOS even thogh I'm not getting smoke but just not feeling confident in getting the Air intake off to access the top hose. Like you ive ordered 25 to 40 stainless jubilee clips instead of the clamps. Getting them off was a task and putting them back would have tipped me over the edge. The old bellows was so bloated it was at least 1/8" to wide at the crank case end . No wonder it was leaking it was crimped up and no way it would seal. Hoping when new one comes its a nice fit top and bottom.

The copies are junk..particularly the bellows, the Porsche one stays soft and supple for many years