Re: AOS Replacement Question

Good-day all,

I have a 2008 Boxster S and have recently been losing about 500mL of oil every 4000km. I decided to take a look at the AOS and once I removed the AOS tubes at the air intake, I managed to get a pinky covered in oil upon insertion. The plastic air intakes also had oil residue on the outside which tipped me off on the AOS. Looks like I found the culprit. On the 2008 S models, can the AOS be removed from the top or do I have to raise the car to loosen something underneath? I was unable to see any screws and/or bolts from the top.

Thanks in advance!

JJ

I can't imagine that 987s are all the different from 986s. I had to put the car up, remove the RR wheel, and access the snap-clip that secures it to the crank-case via the rear wheel well ( and mostly blind). I did post a write-up and pics, here, some time ago, but don't know what exactly became of it.

It may simply be me, but i have never heard of the AoS being a source of appreciable oil loss. Its usually more a source of a drop or two of oil that makes its way through to the combustion intake and creates a cloud. While that looks like a lot, its a tiny volume of oil.

My point is you may have another leak, or it may be a leak around the AoS

Grant

Grant

gee-lenahan-at-gee-mail-dot-com

I have read on a number of board that the AOS is a culprit for oil loss and it may be semi-significant in some cases. I will post some pics of my intake - it is covered in a micro oil film and has attracted dirt on the outer-top of the intake. When I placed my pinky into the AOS tube (at the intake), it came our covered in oil. The odd this is that I do not see any white smoke from the exhaust. Then again, I am not heavy on the pedal. I will post some pics.

Pedro's DIY article indicates that on newer model Boxsters (I think 986 at the time), that the job can be done from the top however someone told me that the car must be raised. Perhaps Pedro can chime in on this one.


Thank you

Quote
grant
I can't imagine that 987s are all the different from 986s. I had to put the car up, remove the RR wheel, and access the snap-clip that secures it to the crank-case via the rear wheel well ( and mostly blind). I did post a write-up and pics, here, some time ago, but don't know what exactly became of it.

It may simply be me, but i have never heard of the AoS being a source of appreciable oil loss. Its usually more a source of a drop or two of oil that makes its way through to the combustion intake and creates a cloud. While that looks like a lot, its a tiny volume of oil.

My point is you may have another leak, or it may be a leak around the AoS

Grant

Although it may seem that way, the AOS is not generally associated with oil consumption.
When the AOS passes oil into the intake you will see smoke come out of the tailpipe(s).
The AOS does collect most of the oil in the engine's crankcase air space in the form of droplets which it distills like an inverse osmosis filter.
But the AOS is not perfect and the diaphragm can have minute tears that allow some oil mist through.
This oily mist will collect in the intake tee as well as in the intake plenums and will coat them with oil, so it's not uncommon to find oil here in a normal car.
Most major oil consumption happens when oil passes through the piston rings.
Happy Boxstering,
Pedro

Pedro Bonilla
1998 Boxster 986 - 311,000+ miles: [www.PedrosGarage.com]
PCA National Club Racing Scrutineer - PCA National HPDE Instructor - PCA Technical Committee (Boxster/Cayman)

---

Racecar spelled backwards is Racecar

"Racing is life. Anything before or after is just waiting" ... Steve McQueen as Michael Delaney in "LeMans"

"If you wait, all that happens is that you get older"... Mario Andretti

"Being second is to be the first of the ones who lose" ... Ayrton Senna

and have mentioned it online a few times. It ties in with my theory the AOS is responsible for the oil that is present at engine start and produces the oil smoke at engine start.

It is my theory the AOS by failing to efficiently remove oil from the crankcase vapor lets a significant amount of oil vapor flow to the intake and from there to the combustion chambers where it is consumed.

That one doesn't see any smoke -- except upon occasion at cold start -- from the exhaust is not evidence the oil is not being burned. Even with the Mazda rotary engine that purposely burns oil -- the oil consumption can be one quart in just a few hundred miles -- to help lube the seals in the engine this high rate of oil consumption does not produce any oil smoke. However I can state that rotary engine exhaust is quite foul and has an unpleasant odor to it the times (not very often thank goodness) I've been behind a rotary engine equipped car.

In the Boxster engine rings get blamed for this oil consumption (and oil smoke upon startup) but the reports I read from owners of cars with high oil consumption the engines do not appear to exhibit the other signs of the rings being at fault. There is no cloud of oil smoke at other times an engine suffering from poor ring seal manifests oil smoke.

Valve seals and guides also another traditional source of oil consumption do not manifest oil smoke at typical times either.

Absent in my experience the very rare engine with bad rings or bad valve guides/seals the AOS is the only reasonable explanation for this source of oil consumption.

The oil the AOS deals with is in vapor form and when the AOS fails to remove this vapor the vapor goes to the engine and as a result the oil burns very well, relatively speaking.

The oil that is responsible for the smoking upon startup starts out as vapor but collects on the intake wall opposite from where the hose from the AOS connects to the intake manifold. The techs I've talked to over the years about this tell me that when they open an engine up to the point the intake is exposed invariably there is oil wetness present in the area of where the AOS connects to the intake. The worst offenders are those engines that have been overfilled with oil.

Upon engine shut down the heat soak encourages this oil to flow down and into the runners for one or two cylinders.

The smoking upon engine start arises from the pool of oil that gathers on top of one or both intake valves (if they are closed) or gathers in the cylinder if they are open and experiences incomplete combustion at cold engine start.

Since the engine is cold the first couple of cylinder combustion cycles will almost certainly not be hot enough to completely burn this oil and thus whatever unburned oil there is is pumped out of the chamber proper and some of it ends up deposited on the cold walls of the exhaust system from which it burns away as these surfaces heat up as the engine runs.

Would I advise an AOS replacement for a high oil consumption engine? No. First of course is this is just my theory and I'm not about to direct someone to spend money he otherwise wouldn't or doesn't have to spend on just a theory of mine.

Also, since I hold the AOS in such low regard -- when it works right it sucks and when it doesn't work right it sucks even worse --- there is no guarantee the new one would be any better than the old one. Thus after spending this money the owner would recognize no decrease in oil consumption and understandably be upset.

The only time I would advise an AOS replacement is when the AOS is clearly showing signs of failing.

All of the AOS versions (986, 987, 996, 997) are very similar.
They have two 10mm hex bolts that hold the base in place onto the engine block.
These bolts are easier (in the Boxsters) to be removed from underneath.
It also helps to remove the passenger side rear wheel. It gives you visibility into the AOS base.
The AOS is also connected to the engine by means of a rubber bellows tube secured with two spring clamps.
These spring clamps are difficult to access so cut through the middle of the bellows with a knife.
The new AOS already comes with a new bellows.
Happy Boxstering,
Pedro.

Pedro Bonilla
1998 Boxster 986 - 311,000+ miles: [www.PedrosGarage.com]
PCA National Club Racing Scrutineer - PCA National HPDE Instructor - PCA Technical Committee (Boxster/Cayman)

---

Racecar spelled backwards is Racecar

"Racing is life. Anything before or after is just waiting" ... Steve McQueen as Michael Delaney in "LeMans"

"If you wait, all that happens is that you get older"... Mario Andretti

"Being second is to be the first of the ones who lose" ... Ayrton Senna

Thank you! Can access it via removing the wheel only? This would save me the trouble of jack-standing both sides of the rear end and crawling underneath the car.

Quote
Pedro (Weston, FL)
All of the AOS versions (986, 987, 996, 997) are very similar.
They have two 10mm hex bolts that hold the base in place onto the engine block.
These bolts are easier (in the Boxsters) to be removed from underneath.
It also helps to remove the passenger side rear wheel. It gives you visibility into the AOS base.
The AOS is also connected to the engine by means of a rubber bellows tube secured with two spring clamps.
These spring clamps are difficult to access so cut through the middle of the bellows with a knife.
The new AOS already comes with a new bellows.
Happy Boxstering,
Pedro.

If you've done it before, the whole procedure can be done from above.
It's harder, but it can be done.
By removing the rear tire you can get to see the base of the AOS.
With a couple of 8" extensions you may be able to remove the bolts from the wheel well.
Then you could cut the bellows and pull the AOS.
I have done it just from above and it takes twice as long and a few knuckles.
Happy Boxstering
Pedro

Pedro Bonilla
1998 Boxster 986 - 311,000+ miles: [www.PedrosGarage.com]
PCA National Club Racing Scrutineer - PCA National HPDE Instructor - PCA Technical Committee (Boxster/Cayman)

---

Racecar spelled backwards is Racecar

"Racing is life. Anything before or after is just waiting" ... Steve McQueen as Michael Delaney in "LeMans"

"If you wait, all that happens is that you get older"... Mario Andretti

"Being second is to be the first of the ones who lose" ... Ayrton Senna

wheel opening and can jack only that side. In fact, as i recall, there is no benefit to jacking the car since you need to get over the suspension, frame and exhaust members that would block you from the bottom. Search for my name and AOS for pics.

Grant

Grant

gee-lenahan-at-gee-mail-dot-com

Here is a pic of the intake plumbing. Notice the darker area on the "T".

Thanks!

Pedro Bonilla
1998 Boxster 986 - 311,000+ miles: [www.PedrosGarage.com]
PCA National Club Racing Scrutineer - PCA National HPDE Instructor - PCA Technical Committee (Boxster/Cayman)

---

Racecar spelled backwards is Racecar

"Racing is life. Anything before or after is just waiting" ... Steve McQueen as Michael Delaney in "LeMans"

"If you wait, all that happens is that you get older"... Mario Andretti

"Being second is to be the first of the ones who lose" ... Ayrton Senna

Really?? That would mean that some amount of oil would always be coming from the AOS - good or bad. Excatly how much oil should be in the AOS tubes that connect to the "T"? The tip of my pinky was covered in oil and was almost dripping. I do not think that much oil should be passing.

Thank you!

Pedro Bonilla
1998 Boxster 986 - 311,000+ miles: [www.PedrosGarage.com]
PCA National Club Racing Scrutineer - PCA National HPDE Instructor - PCA Technical Committee (Boxster/Cayman)

---

Racecar spelled backwards is Racecar

"Racing is life. Anything before or after is just waiting" ... Steve McQueen as Michael Delaney in "LeMans"

"If you wait, all that happens is that you get older"... Mario Andretti

"Being second is to be the first of the ones who lose" ... Ayrton Senna

You can see my droplight going in, and in the top of the pic you can see the cable of the remote-operated hose clamp tool disappearing into the nether regions (aka the base of the A-O_S)

[i44.tinypic.com]

Grant

Grant

gee-lenahan-at-gee-mail-dot-com

I would not do it that way. The extra access to the lower fasteners through the wheel well is a big help. I did not find this job all that hateful but it was a few years ago.

I picked up the AOS this afternoon and took a good look, with a light, in the area. I noticed that the rubber tube on the bottom on the AOS took a 90 degree bend and connected to the engine block. At that point, there was a hose clamp and I figured that I could remove it with a small set of channel locks. This was the most difficult part of the job and took about 35 minutes of getting my left hand to function properly - along with some terrible words. Once the clamp was off, the rest was simple. The E-Torx bolts were a pain as I did not have the sockets for these ($30 bucks later, I had a set). Fortunately, they were easy to remove from the top. I understand that on the older model Boxsters, there are hex nuts that must be accessed from below.

I suppose those with 986 models would have no choice but to do the job from beneath. Fortunately, the AOS mount was change on the 987s to make the job a bit easier.

Thanks to all for the great input!!

Cheers



Edited 1 time(s). Last edit at 05/29/2013 10:57PM by jjspike. (view changes)