AOS, Intermix, both?-FIXED

After moving into a new condo and moving job locations I was looking forward to my first weekend without a project in quite some time. I had a nice day on the slopes until I drove the 2001 C4 back home. On the ride a check engine light popped up. The car was running fine, oil pressure was good, temperature was good, so I figured it might be an emissions issue and I'd pull the code when I got home. I stopped for lunch on the way and when I restarted the car I got a loud screeching/squealing sound. I was about 40 miles from home at this point and figured the AOS had finally developed the problem I had read about. I hoped in to nurse it home and within 20 miles I noticed the car was running a bit rough...the check engine light went to blinking and I immediate pulled over to shut it down. When I shifted into neutral the engine died immediately. I had the car flatbed home. The only codes the ECU stored were misfires on a couple of cylinders (1&3). There appears to be a light residue in the oil fill cap (might just be due to short trips in winter). The coolant seems noticeable darker in color. At this point I suspect an intermix of the oil and coolant. I'll drain some oil and send it out for analysis to confirm. Questions: If the intermix is due to the AOS is it possible to flush the oil and coolant, replace the AOS and move on with life? Any way to determine if the intermix cause additional damage when it shut down (short of a boroscope which I don't have). If the intermix is due to a cracked head, is there any way to confirm this prior to a teardown of the engine? Many Thanks, Shawn

sounds like AOS failed badly check your coolant and oil - that will tell you its not an intermix (no oil in coolant, no coolant in oil) now to change that AOS and get the smile back and the worries gone

Might be cracked coil packs.... as well. The oil cooler is known to fail as well for intermix. If the intermix is bad.... gotta flush out the rads. GL.

after seeing how bad the radiators get from intermix.... I would advise replacing them, its really really really hard to get all the stuff out.... I am hopeful you just have some small issue and will be up and running in no time

I'm wondering about the misfiring codes. I guess I was thinking the worst that it might be coolant in the cylinders causing the misfires. The coil packs were replaced around 60k miles, but it is 108k miles now. Any suggestions on how to confirm it's only the AOS and not a cracked head? Thanks, S.

if it has a big enough vacuum leak it could cause misfire - just hoping for you...Macster has written several really in depth ways to check the AOS... search AOS posts by user - that should get you the info

That loud squeal is indicititve of the AOS failing. Hope thats it! Did temp go up? Did oil pressure do anything up or down?

The oil pressure and temperature were both normal during this process. That was part of my reasoning for not worrying about the initial check engine light. I pulled a sample of coolant last night and it actually looks perfectly clear with no oil residue. That certainly made me feel better about the possibility of an intermix. Next I'll drain the oil and send a sample off for analysis to confirm things on that side. Based on some of Macster's earlier posts about diagnosing the AOS I pulled the intake and took a good look at the throttle body. The body and plate are soaked in oil. That seems to point very strongly at the AOS failing. I'm starting to believe that the AOS failed during my drive. The subsequent oil being drawn into the chambers and the vacuum leak likely caused the misfires that were recorded by the ECU. Finally, when I shifted to neutral at the blinking check engine light the engine tried to reach idle but wasn't able to hold it due to the vacuum leak. That resulted in the engine dying. I'm feeling a lot better about this situation now that it's looking like it's not a cracked head, but just a PIA AOS. I'll feel even better if the oil analysis comes up clean. -Shawn

pull the dip stick and look at the oil, if its "oil color" and noy cream in your coffee color.... I would not even send it out...seriously, in order to have an intermix big enought to throw a CEL your oil would be creamy brown... but if you have coolant in the tank, (not low aka consumed) you are most likely OK.... AOS is not that bad....is this going to be a DIY or "take it in" job....? If it did get oil into the intake I would clean what you can and maybe consider a set of new plugs too

Sounds like the AOS. When mine failed I had large amounts of oil in the intake/plenum. If it is intermix cleaning the radiators is actually one on the easier parts to clean. You can remove them and take them to a radiator shop where then can hot flush them a few times to remove the goo. It is the tubes from the rear to the front of the car and the heater coil that are the bigger challenge. For the tubes I removed all the connecting hoses and used an electrical fish tape to draw rags through the tubes. Probably got 95% of the goo out. The heater coil I just let the system running flush it out. After I fixed my intermix I changed the coolant a few times including using a vacuum device to suck all the coolant out. I am sure that if I tested my coolant there would still be traces of oil in the system due to residue I could not get out. I am not really worried about that. If it was coolant in the oil I would be worried. I have over 10,000 miles since my fix so I am not worried about either these days.

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This post is logical..... GL with the AOS R&R. Lots of diy info here. Let us know how you make out.

1. It seems many people are handling this when the engine is already out. Others suggest dropping the transmission and lowering the engine. Still others are going in from the top and removing the intake. Is there any consensus on this if: a) I have one scissor jack, one hydraulic jack, and four jack stands b) I'm working in a public garage I'm leaning towards going in from the top/side (removing the wheel) since it avoids me having to drop major components in a public area. This is a 2001 C4 MT if it impacts your feedback 2. Is it safe to drive the car in the current condition? I'd like to move it 1.5 miles to a more private garage. Towing is possible, but a huge pain due to low clearance at both garages. I'm think that if I disconnect the MAF it should run roughly but run. Thanks again, S.

I opted to go from the top - Ferd (redridge) made the suggestion... it works OK with minimal tools and about as much stuff as you have for jacks I lowered the motor (rear mounts) enough to gain some space (big help) and the lower bellows clamp almost beat me - I had hurt my hand and cound not squeeze the clamp and install it after at least an hour of trying I replaced it with a worm clamp - but not too tight so it didnt bit into the bellows - overall a pretty easy job - just takes a lot of time OH one other thing, I never liked the way the AOS went on... it just sort of pushes against the block hole to seal, never left me feeling like it went in right - but it did... I wasted a lot of time trying to determine if it was actually in or not

1. go to a garage with some heat.... this will prob take the whole day (8 hours going in from the top). But you still need to get under the car when working on the bellows and mounting screws. a. Make sure they are good stands. Use the jack to put it under the engine end for insurance. Think safety. b. your gonna be on your back for some time... you can drop the engine a couple of inches if you need more room. 2. I dont think you will damage the car going 1.5 miles .... if you keep the revs up. No need to pull the maf IMO.

You will want a set of these for the hose clamp

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

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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.

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

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.

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.

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?

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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.

+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

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.

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.

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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.

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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.

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.

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.

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what exactly is the meaning of THIS !!

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Definitely one of the most helpful tools made, I have a Bluepoint version. Absolutely love it!

Oop's. Did I say other forums. Must have been thinking of those beemer forums

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I agree with you here.... disconnect this pipe and there is no way you can cause oil to go through the intake.... Yes, you should do whatever makes you feel comfortable.

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We do not hear of all engine/IMS failures here. The hydraulic lock up failure is rare. I've only heard of one the one I mentioned, but I always stress the risk. My Boxster has been through 2 of these AOSs and the engine has not suffered any harm. But as I mentioned, I avoided running the engine for too long. Also, the 1st time my Boxster engine's AOS was acting up the engine consumed quite a bit of oil: The oil level went from the max line to just above the min line from burning oil that was being pulled through the AOS. The problem with the oil is it is not compressible and the piston has to reach the top of its stroke before the combustion cycle can begin. So the oil can't burn off before it can do its damage. The other possibility is the intake walls get very wet with oil and this oil as the engine sits drains down into one cylinder. (This is the primary mechanism from which these engines exhibit the smoking upon startup behavior.) Upon the next engine start the engine controller may not be even be triggering fuel and spark on at the cylinder (or cylinders) that has the unfortunate luck to be the gathering place of this oil. Sincerely, Macster.

The Grand Am 3.4 and 3.6 GS cars had hydro lock problems which is why Motorsports created the 2-chamber AOS. I too doubt that under street conditions you could cause a hydro-lock, but they seemed to blow them up regularly in GA until Porsche created the 2-chamber version. That fixed it...

If you are worried about hydrolock plug the aos as described. pull the plugs. you can boroscope or other wise inspect the cylinders. pull the fuel pump relay. turn the car over, see if any oil comes out the spark plug tubes. maybe even put some paper towels in the tubes to absorb any oil that comes out so that there isn't a huge mess. If you get a ton of oil out of one of the tubes -- you saved yourself from hydrolock either way -- put it all back together (except aos plug) and if you want fix the aos yourself or - drive it to your mechanic. mike

BTW, if you do have intermix -- I get concerned about the antifreeze pitting the bearings. I tore down my Boxster S and replaced all wear items when I had my intermix --- maybe over kill -- but 25k miles later -- no problems. mike

I just wanted to provide an update and some thanks on this project. I replaced the AOS by removing the intake manifold and pulling it from the top. It was an annoying job, but it was doable and it resolved the problem. In order to gain more access I removed the coolant reservoir. I suspected this would give me some more working room so I had already ordered an updated tank and cap. After starting on the first few bolds on the intake manifold I realized how much easier things are without the tank in the way. I have a C4 so the fuel filter is mounted between the manifold and the coolant tank. That was providing additional constraints. So in the end I pulled: air intake, throttle body, cross tubes, coolant tank, and fuel filter. That gave me room to remove the driver side manifold and reach the AOS. I couldn't believe how much oil had been sucked into the manifolds. I'd estimate at least 1/4-1/2 cup of oil drained out of the two sides. After getting everything together it smoked liked crazy but it quickly cleared up. I cleared the codes and drove it home. I just dumped a bottle of Techron in the gas tank to try to clean up the carbon and residual oil on the plugs, valves, and combustion chambers from the oil. Thanks for all of the advice and the troubleshooting. Shawn

glad to hear, i am getting mine replaced as well, hopefully fixes the smoke and high oil consumption I have been having.

Good job.... Now you can be one of the AOS gurus here.

OK, WHAT exactly is that tool that I absolutely have to have to do an AOS?

Your life will be much easier with a set of these: http://www.sears.com/shc/s/p_10153_12605_00947390000P -Shawn

Thank you VERY much! See! I never even knew something like that existed, and those spring compression hose clamps are ALWAYS a PITA.

Not only do they help applying force in tight spaces to compress the clamp, but the locking mechanism is a huge help. You can compress the ring and lock it open while you get the hose on the nipple. Release the lock and the clamp tightens up. Like magic...

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if anyone needs a set of these tubes, i have a pair of brand new ones. i'll let em go cheap.