bfutch

got one from Sears for $36.00, it is a God send must have!

Macster

Symptoms indicate AOS has really failed. I'd be leery of runnng the engine any at all. If the AOS is as bad as the symptoms you report indicate it is the engine's already ingesting oil and could be seconds away from a hydraulic lock if you start the engine.

I've had two AOS failures and both times bit the bullet and had the car flat bedded to the dealer for repairs: 40+ miles the 1st time and over 90 miles the 2nd time. Even a mile and half is risky. The 1st time I called a flat bed tow truck and when the driver arrived he refused to back into the driveway and pull the car on the bed with the winch. I had to start the engine and to make the situation even worse there was considerable snow and the snow plows had piled snow up at the driveway exit to the street and of course I got the car stuck. I rocked it back and forth and got it free but the engine was smoking to beat the band. The 2nd time I started the engine up after the car had sat overnight in the motel parking lot. The engine starting smoking and kept on smoking. I let the engine idle long enough to take a pic and then shut it off and called for a tow. I was there when the driver dropped the car off and I wrote on the drop off envelop at the dealer "AOS DO NOT START THE ENGINE" and took a pic of the envelop and the writing to make sure I had a record. The service manager told me they get these in once in a while and round up a few techs/helpers and push the car into the service area without having to start the engine. It was the service manager at this dealer than told me the 1st time to avoid running the engine at all if AOS suspect.

Sincerely,

Macster.

Ubermensch

Dharn-Thanks for the tip. I actually already ordered a set when I read how much trouble people had with the clamps. Any other unusual tools that might be helpful?

Macster--Thanks for the suggestion. I'll definitely give that some thought. If the AOS is truly acting like a giant vacuum leak is there any reason not to disconnect it from the intake tract all together to avoid ingesting more oil?

I'm surprised that with all of the repair posts I see nobody has really done a DIY for this repair alone. There are just general reports on issues and suggestions on fixes. Am I missing this somewhere? There are some DIY that show the parts when the engine is out, but I guess I'm more interested in the process of getting it out with the engine in place.

I'm going to get this thing ordered up tomorrow. Are there any other parts I should consider while I'm ordering it? I've heard the bellows should be replaced at the same time. Should I pick up any of the connecting hoses or clamps?

-S

pterfloth

The AOS I ordered from Pelican Parts came with the bellows. I had ordered a bellows without knowing that so it is sitting here. If you want it, its yours.

Do some searching for AOS DIY replacement. I found a few but have deleted the links already.

Good luck! I did mine with the tranny off.

Quadcammer

Do not run the car, especially if there is a chance you have coolant in the oil.

the glycol in the coolant does an absolute number to engine bearings.

Ubermensch

The more I thought about the device and how it works the more I question whether an intermix is even possible during it's failure. Yes, coolant flows through the device, and yes, some oil is in the device, but it's primarily air and coolant that are present. The oil is really just vapor until it's condensed in the unit isn't it? That said, how much coolant and oil can really be mixing? It seems like a minimal amount that would be quickly introduced into the intake and combusted....

All that said, I have a pretty good coating of oil in the intake. Where is this all coming from? Does the failure create enough of a vacuum to extract oil out of the rest of the system and introduce it into the intake?

redridge

The AOS essentially cools the vapors before going into the intake, takes the air bubbles out of the oil and dumps the oil back into the crank case.... if there is a crack in the AOS coolant wall, it can potentially drop coolant in the crank case. There is more than just a coating of oil that goes into the intake. There are plenty of reports here on RL that states plenty of oil are in the intake during normal use (and at the track). Lots of people run a .5 quart less because of this.... also, oil can climb up the AOS column and gets suck up via the intake due to hi G's etc... this happens with a functional AOS and not necesserally a failed one.

ivangene

+1 for 0.5 quart low ... in fact I rarely ran the 996 above 3 of those little lights on the display at start up... I run the 3.2 just at the point where the level indicator bounces once in a while....and check it often

Ubermensch

Okay, I've ordered a new AOS, coolant tank and coolant cap. I figure after 100k miles it's probably time for a new tank despite the lack of leaks. I'm also hoping it will give me a little more working room.

For those that went at this from the top, did you have to remove the driver-side intake manifold or were you able to lower the engine enough to avoid that? I see one DIY on a 997 in which he loosened the manifold but when he wasn't able to get it past some fuel lines he left it in place. Any tips?

S.

Dharn55

You can disconnect the AOS line at the plenum and use rubber plugs to plug the holes at both the line and the plenum if you need to drive the car a little. Won't run perfectly but it can be done. You would have to have a huge amount of oil to get a hydro lock. When my AOS failed I had large amounts of smoke on start up and the oil in the plenum was thick, but never a hydro lock.

With an intermix the coolant in the oil is definitely not good for the engine, bearings and all. But I can tell you this. I had an intermix due to a cracked head. I did not discover it until the coolant light flashed, and by that time the coolant was literally as this as pudding and the oil was thick like a chocolate shake, the coolant/oil mix was emulsified in both systems. Who knows how ling the intermix had been going on, but it had to be for a while. I was told that there was no choice but to replace the engine. I was told that the bearing were ruined, etc. etc. etc.

Well I took the head off the engine and had the crack fixed, flushed the oil system and the coolant system. Reassembled everything. I now have 10,000+ miles on the engine since the fix and the car is running fine. So I am sure the bearings are not as good as they would have been without an intermix, and maybe I won't get 200,000 miles on the engine. But based on what it cost me to do the fix (acknowledging that I did the labor myself) those 10,000 miles are the cheapest miles I have put on the car.

I have had a couple of 928 in the past and I know guys who ran them out of oil, let them cool down, refiled them and off they went for many more miles. What can I say.

Macster

I would not advise running the engine. The engine can be closer to a hydraulic lock than you might believe. It doesn't take much oil.

In the case of the my Boxster's 2.7l engine, the cylinder's displacement is 2.7l divided by 6 or 0.45l or 2700ccs divided by 6 is 450ccs. At 11.5:1 this is reduced to approx. 39ccs or approx. 1.32 ounces (US liquid) or 2.64 tablespoons.

For a 3.6l engine the cyl. displacement is 600cc and this reduced by 11.5:1 is 52ccs or approx. 1.76 ounces (US liquid) or 3.52 tablespoons.

During what proved to be the 1st AOS problem with my Boxster, I called the service advisor to arrange to bring the car in and after asking me to describe the symptoms and what I had done he told me it sounded like the AOS.

He strongly urged me to *not* drive the car. I wanted to. I was out of work at the time and a large tow bill was not something I wanted to add to the cost of getting the car fixed. I listened to him though and bit the bullet (and waved goodbye to approx. $150) and had the car flat bedded to the dealer.

Later I talked to service manager and he told me of another Boxster owner whose car was having the same symptoms and who declined to follow the service advisor's advice (owner said something to the effect I bought the car to drive and I'm going to drive it) and continued to drive the car while waiting for the parts to come in. While he was driving the car the engine suffered hydraulic lock.

In fact, when I returned from an out of state trip (and with -- thank goodness -- a job offer) and went to pick up the car, I was aghast to learn that the engine had been subjected to a compression test *before* the AOS was replaced and during this test had suffered a mild hydraulic lock. What I guess saved the engine is that only one cylinder was affected and it was the one that was being compression tested at the time. The other cylinders were running sans spark plugs.

At this point the car was long out of warranty (had around 78K miles on it) and had the engine been destroyed I'm not sure who would have been responsible for the engine.

After objecting to this charge with the service advisor I then spoke with the service manager and said that had I been given the chance to accept or reject the test I would have most certainly rejected to have the test done. To his credit, the service manager removed the cost of the compression test from the repair bill with no further discussion.

The 2nd time the AOS acted up I left nothing to chance and reached for the phone and arranged to get the car towed to the dealer (same dealer). This time I was there when the car was dropped off and wrote on the drop off envelop "do not start engine".

I would not advise anyone who believes his car is undergoing an AOS problem to run the engine at all let alone drive the car any distance.

Sincerely,

Macster.

Macster

I can't advise you with any degree of authority regarding any disconnecting the AOS or doing anything else to avoid the engine ingesting too much oil from a failing AOS other than to simply not drive the car, avoid starting/running the engine, even at idle, until the AOS has been replaced or eliminated as the source of the symptoms.

Sincerely,

Macster.

Ubermensch

Given the potential risk of damage, and the minimal reward of my comfort I'll take your advice and avoid any driving. Thanks for your continued input.

Also, I was complaining that I couldn't find a good write up on the process and then finally found this thread:

https://rennlist.com/forums/996-foru...separator.html

I figured I'd link it here to aid someone in the future.

S.

Dharn55

I don't mean to be too argumentative, and I have a lot of respect for Macster and his experience with Porsches. But with all the AOS failures that have happened, and AOS failures are pretty common, I have never heard of a hydro lock caused by an AOS failure, here, on any of the other forums, mentioned by Jake Raby, or any one else for that matter.

I would think that if this type of failure was occurring we would have heard of it, we certainly here of just about every type of failure that does occur on a regular basis. For 3+ tablespoons of oil to be drawn out of the AOS, through the plenum, through the intakes and into one cylinder, and not burnt off during the combustion and exhaust strokes implies a huge amount of oil. IMHO

And if you disconnect the line from the AOS to the plenum you have cut off the source of the coil. Then again, a couple of hundred dollars for a tow is not that bad to prevent potential damage to a car.

ivangene

what exactly is the meaning of THIS !!