Maclen

Thanks all..Ok men here's the scoop, had car idleing, oil cap unscrewed with ease, only sight sound change in idle, should rule out the AOS...your thoughts?

Macster

The cap removal test is not infallible.

Besides, by the time I got to the cap test -- stumbled upon it by accident in trying to diagnose during what proved to be my car's 1st AOS failure -- there were other symptoms. The engine was not running right and the idle was going up and down, while not a lot I knew this was not normal behavior.

However, based on what you wrote in your first post just a brief bit of smoking under the conditions you described doesn't give me any reason to believe the AOS is bad or going bad.

Of course, based on my most recent experience with my car the AOS can go from apparently just fine to bad in very short order.

If you want for additional peace of mind have the car checked out by a tech.

You do realize though that you can have the car checked out every day but the AOS will almost certainly at some point fail. As I mentioned above how suddenly my car's AOS went from ok to not ok with no forewarning the AOS could fail at any time after the tech checked the car that day to just before the tech checks the car the next day.

All you can really do is be aware of the possibility the AOS might go bad and if (more like when is my experience) it happens recognize the symptoms/signs and take reasonable precautions to guard against doing any damage to the engine and get AOS taken care of.

Afterwards the engine will be no worse for the experience.

Maclen

I should add no smoke today at all, I just drove it 45 minutes getting on her, runs like brand new.
smooth idle, plenty of power and not a hint of vapor of any kind, all lights dark, temp steady at 175.
putting it up for the winter in 2 weeks in heated storage, usally do an oil change, will the AOS throw a code?
will have it checked, I think the wife got the smoke at start up and got nervous because it's never don it
in the 3 years we have had it, will just watch it. thanks

sjfehr

AOS only throws a code if the oil causes misfires or emissions issues. If your AOS failed, you'd know it; there's no "I wonder if my AOS is bad?" because it'll be smoking like it's a cartoon- you won't have to ask, you'll KNOW. It's not subtle at all, when it goes, it GOES. There's another mode where it just makes a godawful whining noise, but you don't have those symptoms. What you're reported thus far just sounds like perfectly common and normal 986 behavior.

Macster: stop overfilling your oil!!

Maclen

Thank you..have a good wekend all

Macster

By all means, change the oil/filter before you put the car away for the winter. Be sure you drive the car to thoroughly spread the oil about in the engine and in the lifter bodies which can take some time to exchange their "old" oil for fresher oil.

The AOS may or may not cause a code to be thrown.

In the 3 AOS failures now only once, the 2nd one, did any error codes appear. I do not recall what they were now but I attributed them to a failing MAF. The engine still ran just fine -- I was on a 2K mile trip and the CEL came on at the end of the day as I was leaving the freeway for the night. My diagnosis of MAF proved to be wrong, obviously wrong, when upon the 1st start at the hotel in the morning the car just smoked and smoked and smoked. It then dawned on me that my "diagnosis" of MAF was wrong.

The 1st and 3rd AOS failures didn't generate a CEL at all. Given how badly the engine was smoking the other day I wouldn't have been surprised if perhaps the DTC came on due to misfiring but it didn't light up at all.

'course, I didn't give it much time. As quickly as I could I got to where I could park the car and have enough room for the tow truck and then shut off the engine.

Macster

What in the world prompted this? I do not overfill my engines with oil. Generally the oil level is a bar or two down and I only add oil -- a quart -- when I'm sure there is room for it without overfilling the engine.

sjfehr

Overfilling your oil is a surefire way to cause the AOS to fail. 3 failures is probably not a coincidence.

Macster

Not sure where you got that idea overfilling the engine with oil is what causes AOS failures.

3 failures is not a coincidence with over 285K miles on the car. It is the result of having driven the car over 285K miles.

As I mentioned before the first AOSMore failed at 80K miles. Average miles? My impression most Boxster AOS's fail before 80K miles.

The 2nd AOS failed about around 100K miles later. I had hoped the replacement for the 1st AOS would last forever but no such luck. Still 100K miles…

And the 3rd one lasted about another 100K miles.

There have been lots of AOS failures and I dare say the majority of them occur before 100K miles. The oil level plays no role. The things just develop material fatigue and the rubber diaphragm cracks or splits or develops a leak and that's that.

sjfehr

It's been a common theme in many AOS threads, I assumed you'd picked up on it too. Wouldn't be surprising that high oil levels would lead to an increased risk of quantities of liquid oil getting sucked into the AOS and damaging it. The e-dipstick seems to be the primary culprit as it often reads inaccurately low and encourages people to accidentally overfill. Better to overfill and risk AOS damage than underfill and risk IMS damage, but there's a sweet spot in the middle, just a tick below full, that seems to be the best.

Out of curiosity, what level do you usually maintain your oil level? I usually put mine just a tick below full. The one time I slightly overfilled, my AOS went out a few weeks later. I did not repeat that mistake.

Macster

No, I never picked up from the AOS posts that overfilling the engine with oil was a contributor to AOS failures or really any other problems though it should be avoided for reasons I'll cover below.

The Boxster AOS doesn't get damaged by what passes through it, it gets damaged, that is suffers from the constant flexing the reinforced rubber diaphragm experiences.

In your car's case the slight overfilling of the engine with oil and AOS failure was just a coincidence.

Over time the AOS just wears out and it does so on such a way that the smoking that I observed the other day is one result of that.

The 3 primary factors that play a role in when the AOS wears out are the type of usage the car gets, the average/overall condition of the engine oil, and any variation in the quality of the unit.

For the type of usage it would be usage that had the AOS diaphragm more frequently being flexed. One type of usage that comes to mind that would do this is track usage. I note there is a motorsport AOS available which suggests Porsche recognizes track usage is harder on the AOS than plain old street usage.

If the average/overall condition of the oil was poor because the oil was not changed often enough for the type of usage the car received, this could result in a larger than average build up of acids in the oil and these acids would attack the diaphragm (among other things) and could help bring about an early failure of the AOS diaphragm.

Last but not least perhaps is the quality of the AOS. I'm talking about the normal variation in quality any manufactured part/assembly can have.

As for overfilling the engine with oil to somehow avoid IMSB damage is, I'm sorry to have to say this, but this is just silly.

If there is anything one can do to help prevent, or postpone, an IMSB failure, the only thing that I can think of would be to change the oil/filter on a schedule that agrees with how the car is being used, which unfortunately would have those who drive fewest miles over a given amount of time changing the oil more frequently than those who drive the most miles over the same about of time, which again is unfortunate because it is contrary to how most people think about oil changes if they even think about them at all.

More frequent oil changes helps keep the acid level in the oil down and the oil being fresher has a more active additive package which helps keep the AOS diaphragm more pliable and flexible. POA oils are unfriendly to seals. While the AOS diaphragm is not a seal it is similar to one in its makeup. To counter this oil companies add compounds that are seal friendly. Ester is one such compound. But if the oil is run too long this ester (which constitutes just a small percentage of the oil's makeup) gets depleted and the POA's inherent unfriendliness to seals and in this context the AOS diaphragm begins to take a toll.

There is potentially a risk to overfilling the engine with oil. For one thing the e-oil level system is not intended to report how much over full the engine is with oil, only that it is too full, above the max line, so one can't know by how much the engine is overfilled.

If the engine oil level is too high this can result in oil in the sump overtopping the oil baffles and allowing aerated oil to get into the area enclosed by the baffles -- which are designed to help keep oil around the oil pump pick up but to also prevent aerated oil from entering this area.

If this happens this can result in the oil pump pulling in this aerated oil which can be death to the crankshaft main and rod bearings. And there is no benefit to the IMSB so this overfilling is not only for naught regarding any benefit to the IMSB but actually puts at risk other expensive engine internals.

Oil that is returned to the sump can still be aerated. The oil can have different levels of aeration with the upper most layers of oil begin the most aerated and the bottom most layers the least aerated. It is the bottom most oil the baffles are intended to allow into the the enclosed space around the oil intake.

The oil level should be kept above the min line and up to but not above the max line. I would never let the oil level get so low that any kind of warning was issued.

Ideally the closer to the max line without going above it is best. This means the engine has the most oil volume and thus the oil has the most time to shed any air before it is recirculated through the engine. Under high g-forces, high RPM usage, the engine stands the best chance of always having sufficient oil available to the pump. The additive package is the strongest and more able to counter the build up of acid.

The oil level I try to keep is I stated above: Above the min line and up to but not above the max line. In most cases I will let the oil level drop to where I know adding a quart will bring the level up to but not over the max line. In the case of my Boxster it takes several thousand miles of my type of driving to have the level drop this much. In fact sometimes I add oil, top up the oil level, not too miles before the oil/filter is due to be changed on miles.

However, before venturing out on a road trip I will top up the oil adding less than I think will be required and doing this one or more times in order to bring the level to the max line without going over it so the engine starts out with a full load of oil. Adding oil at this time and this precisely gives me a chance to monitor oil consumption over a number (often 4K or more) miles of driving in a short period of time (sometimes just a few days).

extanker

non stop

sjfehr

Have you ever actually taken your AOS apart and looked at it, Macster? It's not acid vapors causing it to fail, I can guarantee you that much. I suspect in your attempts to keep your oil always filled to the max line you're inadvertently overfilling it; you know as well as anyone here that the oil level changes depending on when you read it. It's OK if it's a tick below.

And your theory about white smoke on startup is incorrect, sorry. White smoke on boxsters parked cold but not parked hot is 100% reproducible.

Macster

While I've been a strong advocate of frequent oil/filter services to keep the acid level in the oil down, I do not think I claimed acid vapors are causing my AOS's to fail. I have to point out that the shortest lived one lasted 80K miles. The others have gone around 100K miles. They wear out, not from acid, but just material fatigue.

I haven't cut this latest AOS apart but I suspect it will show the same failure sign as the first one I cut apart. The diaphragm is cracked/split.

Given how little hardware or moving parts are in one of these things there's not much else to fail.

While I like to keep the oil level up to if not at the max line close to it, the oil level spends more time below the max line than at it.

Furthermore, I'm quite adept at checking the oil level using the electronic level system and I have every confidence the oil level is not too full. It is clear when this is the case as the bar above the max line is on. Also, when I change the oil I can also use, and do, the dipstick and both oil level measuring systems agree on the oil level, at least that it is not above the max line.

Even if the oil level were too full, I fail to see how this would cause the demise of the AOS.

Last but not least, I do not know what you are referring to regarding my theory about white smoke at startup. I can assure you the oil is not getting past the rings after the engine is shut off. There is no reason for oil in the cylinder to force its way through the tiny gaps in the rings towards the hotter part of the engine. Oil when given half a chance flows away from heat. As I have said before, one can see this when heating a small amount of cooking oil in a skillet. As the skillet and oil heat up the oil flows away from the hotter spots and collects in the cooler spots.

This leaves the AOS as the source of oil. The techs tell me that almost always when they expose the intake system of a Porsche engine the intake walls near where the AOS hose connects are wet with oil and the oil is present on the intake walls even if the engine is not overfilled with oil.

DennisAN

The other oddball thing about the AOS is their altitude sensitivity. According to Jake Raby, they never fail around Denver or other high-altitude places. Livermore is basically at sea level. I see lots of reports of AOS failures from flat Florida owners.