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Old 01-18-2014, 05:07 PM   #1
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AOS replacement tips

I know this has been DIY'ed before, but this captures some key points in replacing your Air / Oil Separator, and will hopefully help you avoid similar problems and frustrations.

I accessed the bolts and bottom bellows hose from under the car. Remove the right rear wheel. Prop a LED light in the left side of the opening. You only have room to get your right arm in and see what you're doing at the same time. To make more room to work on the bottom hose connection, pop off the wiring connector right in the front of it. Also remove the connector mounting bracket just below that (10mm bolt), and wire it out of the way. I also disconnected the oil filler hose near the intake plenum, to give me just that little bit more room to work.

REMOVING:

- Removing the top hose is easy. Compress the "grips" on both sides and wiggle it off. (I managed to break off the grip ring, I think during my coolant tank replacement gyrations, so be careful.)

- Getting the plastic connector off the middle of the AOS (towards passenger side) was a real pain, as I couldn't really get a good grip on it when accessing from the top or underneath. After struggling with this for a while myself, I had an assistant, working from the top, put pressure on and wiggle the hose towards the passenger side while I worked to compress the release tabs from under the car. Be very careful that you don't break this connector!! Replacing this hose is a serious pain.

- Bottom rubber bellows hose: my new AOS came with a new one, so, because the clamp is so difficult to get to, even with my remote clamp pliers, I just cut the bellows (careful with your knife in there!). Once the AOS was out, getting the remainder out with the remote clamp pliers was much easier.

- Remove the 10mm AOS mounting bolts. From the top, pull the AOS away from the engine to free the nipple going into the engine, and move the entire assembly up and out of the car.

INSTALLING:

I made a huge mistake and tried to re-use the clamp on the bottom bellows. To those that have done it, I bow down to you. I got a replacement screw-type clamp, which made the job MUCH easier. I made sure that the new clamp width was equal to or less than the existing one. Make sure it's stainless, to avoid having it corrode and break. There are clamps available that have rounded edges; consider that too.

- clean up as much as you can in the area. Good practice and helps avoid getting crud into the engine-side nipple. Be careful you don't get crud into the engine openings.

- Once the new AOS is essentially in place, with the nipple ready to go into the engine, put in the two 10mm bolts and tighten (DO NOT OVERTIGHTEN). That will pull the engine nipple in.

- The hose bellows, with the new clamp sitting conveniently up and out of the way, can now be finagled onto its pipe. The clamp can then be easily lowered down and into place. I admit that, with only one hand access, tightening the clamp at first is a bit of a pain, until it's tight enough not to move. But still WAY easier than the original clamp.

- Remount the wiring connector and connector mounting bracket.

- The mid and top hoses can now be pushed on from above. Make sure you hear an audible click to make sure they're properly seated. The mid connector is a bit difficult to push on; I used a pry bar that I VERY CAREFULLY used to get enough pressure to get it to click into place.

DONE.



This is the hole you get to work from under the car, accessed from behind the right rear wheel. It's about 6 inches. I lay on my side and used my right arm.

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Last edited by clickman; 12-16-2014 at 07:47 AM.
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Old 01-24-2014, 12:26 PM   #2
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Sorry but what the heck is an AOS?
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Old 01-25-2014, 09:02 AM   #3
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Air Oil Separator
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Old 01-25-2014, 09:37 PM   #4
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Geez, glad I posted this...

Search Air oil Separator or AOS and you'll see that this is a frequently-replaced part that you can save a lot of money on by doing yourself, with the right advice. My hope is that my tips would be the right advice.
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Last edited by clickman; 01-25-2014 at 09:40 PM.
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Old 01-26-2014, 02:10 PM   #5
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....tried to re-use the clamp on the bottom bellows. To those that have done it, I bow down to you...

Thank you, thank you...AND...I did it all from the top!

I must admit that confessing to my sins still wouldn't get me absolution after the words I used during replacing my AOS.
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Old 03-12-2014, 10:46 PM   #6
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Hi Folks,

Can someone confirm the part number for AOS is below? so I need to buy 2?

996-107-080-54-OEM @ $37
Air Oil Separator (Inside Oil Sump of Engine, 2 per car)

I also found another part at pelican which is much more expensive $137
996-107-023-04-M100

Which is the one that is a common failure?
my car is a 2001 Boxster Base Tip.

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Old 03-13-2014, 07:46 PM   #7
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The second
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Old 01-27-2015, 09:17 PM   #8
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Suggestions for easier AOS installation

clickman...you had a great writeup. It helped me a lot. I'd like to add some comments.

1) The middle clamp is much easier to remove after you disconnect the lower (bellows hose) clamp first and can pull the AOS almost out. Then, you can easily grip it.

2) I used some baby Vice Grips for the lower (bellows hose) clamp. I may have just lucked out as I snagged the clamp the first time. I ordered some remote clamp removers and they didn't work worth a damn.

3) I used the same type of clamp for the lower bellows, but had a little plastic handle holding the clamp open. You can buy both a new clamp and the plastic handle for way under $10 on ebay.

Otherwise, thanks!

-ed

Last edited by Edslittleworld; 01-27-2015 at 09:21 PM.
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Old 01-28-2015, 07:31 AM   #9
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I did the AOS on my '03 S (three chain engine) this past weekend. The later AOS mounts differently than the early engines and it was a piece of cake. There are two hex head bolts that mount it to the head from the top, the two snap on PCV fittings, and a spring clamp on the hose underneath (this is in place of the bellows on the previous AOS). On this engine I found that it was easiest to access the hose connections from the top. First I released the plastic snap on fittings, then used a small vice grip pliers to get the spring clip. I left the vice grip on the clamp until the clamp was on the new AOS, then released it. MUCH easier than using a spring clamp pliers. That work was done leaning over from the driver's (left) side of the car. At first I tried to get at it from the right side and from below, but it was easier from the left side. Last I removed the two mounting bolts (working on the right side) from above and pulled it out. That process took me about a half an hour, but I could probably do it in 10 minutes next time. Carefully removing the plastic snap connectors is the toughest part. The car now has 52k miles and from what I can tell, the AOS looked to be original.

My symptoms were an occasional plume of oil smoke at start up, a slight rough idle when cold and intermittent resonance (noise). That all seems to be gone now.

So, if you have a late three chain M96 (M96.24 in my case) don't bother jacking up the car or putting it on a lift to swap the AOS. It is MUCH easier to do it from the top.
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Last edited by Qmulus; 01-30-2015 at 09:22 AM.
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Old 01-28-2015, 08:30 AM   #10
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Sorry to ask, but do you have any pictures?
The process will be the same on a base 2003?
Thanks
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Old 01-28-2015, 09:22 AM   #11
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Quote:
Originally Posted by Slate 01 View Post
Thanks for an actual answer, rfuerst.

I've never understood why some just have to give smart@$$ answers when asked. Those types must have had their @$$es kicked continually as they were growing up and now they can hide behind a keyboard and act stupid.

Anyway thanks again.
First ever forum experience for me and was shocked as well.To be honest I am extremely hesitant to ask many simple questions for that reason. Subsequently I have to read and search many unrelated post/threads to get the answer, which is fine as well.There are MANY non butt-licks on here that are extremely and helpful as well
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Old 01-28-2015, 02:00 PM   #12
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Originally Posted by nicecar View Post
First ever forum experience for me and was shocked as well.To be honest I am extremely hesitant to ask many simple questions for that reason. Subsequently I have to read and search many unrelated post/threads to get the answer, which is fine as well.There are MANY non butt-licks on here that are extremely and helpful as well
feel free to ask any question.
you will find more people willing to help then those who don't.
with that said, before i even got to this forum, i got the 101 and the Bentley book.
didnt stoped me from asking stupid questions like what is a "dead blow hammer" or what is "snake oil"

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Old 01-28-2015, 06:42 PM   #13
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Originally Posted by EJ-Fresno View Post
Sorry to ask, but do you have any pictures?
The process will be the same on a base 2003?
Thanks
No pictures. Honestly, it is pretty dead simple. The toughest part is carefully releasing the plastic clips on the plastic hoses. I did that by hand, as I wanted to make sure not to break them. My mechanic friends like to run a right angle pick around the fitting to clean oil/debris from the inside of the fitting. You will need a long extension to get the hex bit into the bolts that attach the AOS, and I used a magnet tool to remove them just to be sure not to drop them. I also used it to put them back in. As I said in my post, a small vise grip was perfect for compressing the spring clip while removing the AOS.

I will say that for the first time since I got it I bothered to undo the clips and put some bolts in the linkage put the clam shell in full service mode. That does make access a bit easier. Honestly, I spent more time typing this than I did actually changing the part.

FWIW, I absolutely LOVE working on this car. Compared to working on my Audi A6 2.7T, this thing is a treat!
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Old 01-28-2015, 07:08 PM   #14
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Did you change only the AOS or you changed some hoses at the same time?
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Old 01-30-2015, 07:41 AM   #15
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Great read!
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Old 01-30-2015, 09:20 AM   #16
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Originally Posted by EJ-Fresno View Post
Did you change only the AOS or you changed some hoses at the same time?
Me? I just changed the AOS, the hoses all seemed fine. I do plan on cutting open the old AOS to see what fails, but I am not in a hurry to do so at the moment.
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Old 01-30-2015, 12:40 PM   #17
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I've deleted a bunch of posts in this forum. Frankly, I'm disappointed. There's no such thing as a stupid question - we all at one time didn't know what an AOS (Air-Oil-Separator) was. This is not the proper tone for this forum - it's an open and nurturing environment where we all can learn. Let's keep it that way.

-Wayne
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Old 01-31-2015, 07:10 AM   #18
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Qmulus when you get around to cutting open the AOS it would be great to see some pictures.
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Old 01-31-2015, 09:38 AM   #19
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Originally Posted by Qmulus View Post
Me? I just changed the AOS, the hoses all seemed fine. I do plan on cutting open the old AOS to see what fails, but I am not in a hurry to do so at the moment.
I was looking for some AOS pictures once and came across this post on Rennlist. It shows good detail of the inside of a failed one:
Another 996 down - Page 8 - Rennlist Discussion Forums
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Old 01-31-2015, 10:16 AM   #20
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Me? I just changed the AOS, the hoses all seemed fine. I do plan on cutting open the old AOS to see what fails, but I am not in a hurry to do so at the moment.
I think there is a diaphragm inside that fails, the aos is just a glorified PCV
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