996 Air Oil Separator replacement

[996C438]

There is a tiny vent hole in the AOS housing . When going to the UAOS that vent hole has to be sealed . I did mine with the AOS on the bench . There is a small channel where the hole is . I filled that channel with RTV . Unfortunately I don't recall if you can reach that channel if the AOS is installed on the car .

If/when the AOS diaphragm cracks/splits the UAOS just keeps chugging along . The diaphragm being up by the throat body " almost " guarantees that oil will not get sucked into the intake . The reservoir/accumulator included with the UAOS is the final piece of the puzzle keeping oil out of the intake . I recommend the track version as it self drains any accumulated oil back to the crankcase.

[aboyandhisdog]

Just a quick post to reiterate some of which has already been said. I have a M96.05 in my 997 and the AOS is something that has been bugging me...is it good, is it bad??? So bought a new oil cap for the car and took the old one (which is good) and also bought a cheap mamometer at Amazon for about $30. Installed the line from the mamometer to the cap so now have a valuable tool for about a total of $60+- which allows me to check and track the condition of my AOS.

You set the mamometer for inches of H2O and a reading between 4-6 is in the ideal range. Mine was 5.33 which is good. Below 4 may mean you have a vacuum leak in a line or fitting somewhere, and a reading over 6 would indicate that you have a bad AOS.

Since this is a fairly well known weak point for these engines and can potentially have horrible results if not detected in time, I feel like this is an easy test that anybody can do for their car. At the very least, have your mechanic check it from time to time and you can take measures before it goes south. You may sleep better knowing it's good!

[911-Purist]

Since this is a fairly well known weak point for these engines and can potentially have horrible results if not detected in time, I feel like this is an easy test that anybody can do for their car.

My thoughts exactly and one that can be done easily instead of replacing an AOS which is quite time consuming on our cars. A one minute check versus an hour-plus for a possibly un-necessarily replacement of a part.

Before the AOS failed on my 991 (MA1), I wanted to confirm the reading of -14 to -16. I got -14.91.

2024-05-06 - AOS (-14.91).jpg (1.61 MiB) Viewed 725 times

[911-Purist]

Since this is a fairly well known weak point for these engines and can potentially have horrible results if not detected in time.

I know about hydraulic lock, but the scene at 1:20 in the following video is a bit far fetched. How does an intake port fill to the brim if an engine is running and the intake valve is opening and closing countless times per second. And if you had that much oil, you would be blowing smoke big time. And why only in one cylinder? A bit of sensationalizing!

https://www.youtube.com/watch?v=DN3upe6AuVI

[aboyandhisdog]

Quick question since we're talking about AOS symptoms and whatnot. One indicator of a failing AOS is said to be oil in the plenum. Now, I have a good AOS but I do have a light coating of oil in the plenum. I want to believe that this is perfectly normal, but I wouldn't mind hearing from others as to whether or not you have an oil free plenum or if a light smear of oil is to be expected. It isn't' much - maybe like you took a small paintbrush of oil and just swiped it around the bottom of the plenum, but it has always perplexed me somewhat. Thanks for the input! -Tom.