tedfromohio

Had the IMSB and RMS replaced in my car last week. Had new tires installed and an alignment done while it was there.

Picked the car up on Thursday and on the way home notice it was pulling to the right. No big deal, he will fix it. Drove the car a couple of places during the day and noticed that once when I started it, there was a huge cloud of smoke! Stopped and got out - it was coming from the exhaust but quickly stopped. Immediately called the shop and he said that it was probably condensation since it stopped so quickly.

Restarted the car later and no noticable smoke, but while sitting at a traffic light, a cloud enveloped me (I thought I must have been sitting next to a diesel truck) when I realized it was my car, I returned it to the shop (I was close by at the time) and left it there over night for him to look at in the morning.

I was there in the morning when he arrived - we started the car and again, a big cloud of blue smoke, but it quickly went away as the car idled.

I am getting paranoid now - not too happy but still confident he will fix it.

He commented that it is possible that there may have been some oil in the crankcase from the engine sitting on a tilt while the car was on the rack for a couple of days getting the IMSB replaced, and now it is just burning off, but he would look at it and have the alignment checked.

Late in the afternoon he called - alignment was spot on (although he did adjust the toe in a slight bit he said) and as it is a C4, I needed to be aware that it might pull a little to one side on occasion???? Then he said there appeared to be nothing wrong with the car and it wasn't smoking any more - I could come and get it.

Like I said, I am a little paranoid now. I am out of town and can't pick up the car until Monday so we will see if it smokes after sitting all weekend. I have heard a lot about AOS failures and am not sure if the symptoms are the same as what I am experiencing. He advised that he checked the AOS when the car was apart and that it looked fine - no need to replace.

I have had several people tell me he is "the guy" and knows his stuff. From my interactions with him, I am betting they are right. I am just a little gun shy and very paranoid at this point. Looking forward to getting car back on Monday seeing how it drives at that point.

kromdom

http://www.renntech.org/forums/tutor...for-a-bad-aos/


I know its easier said than done but...enjoy your "new" car, man

OGWGFIW

That stinks. Hope it turns out well. But I have to ask if you even read the numerous responses that advised you just put a new AOS on when you asked what else you should do while the engine was out? If you would have listened to that advice you wouldnt be worrying about this relatovely inexpensive component now.....and going forward.

I don't know how you "inspect" the sealed unit AOS. Per the recent Excellence write up Porsche has no definitive test for this, so they borrowed a BMW test method using a slack tube Manometer. Did your guy really go to that extent or blow smoke up your rear?

chsu74

AOS replacement adds another hour of labor or 1.5hrs while doing IMS bearing replacement. You can also check if the oil level is too high because the car should run at 1/2 on the dipstick or less to avoid smoke during start up.

You can also remove the oil filler cap when the engine is running. If the car stalls, then the AOS is bad.

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Macster

Sigh. Pulling in any direction after an alignment is a sign the alignment was not done right, with one possible exception, make that two possible exceptions.

If the caster is different between the two front wheels this can result in pulling. Caster is not adjustable, but does not get out of adjustment unless there is suspension/steering wear (on one side) or there's been some kind of accident that has changed the caster on one side.

However if the tech spotted this caster issue he should have informed you and cautioned you that the car might pull in one direction or the other.

Another possible explanation is some alignment shops align the car to compensate for road crown. On a road that is not crowned, or in a lane that is crowned in the other direction this can have the car pulling. I prefer my cars be aligned with no road crown compensation because I drive in areas where road crown is inconsistent or absent or wrong and I can deal with road crown pull.

What were the before and after alignment numbers?

The numbers should show this, in fact if the caster was off the tech should have informed you and cautioned that the car might pull because of this.

(BTW, my Turbo is of course AWD just your car and my Turbo doesn't pull after an alignment. If it did I'd whip it around and head back to the shop in a heartbeat and get corrected.)

Just to be clear, I'm talking about consistent/persistent pulling, not the intermittent pulling one encounters upon changing road surfaces and the fat/wide tires interacting with the road surfaces.

As for that smoking...These engines at various times, in various climatic conditions will emit, can emit, copious amounts of water vapor.

There is one big difference: water vapor dissipates quite rapidly before your eyes while oil smoke persists even in a breeze. I have on occasion (and with some embarrassment) followed a huge cloud of oil smoke from one of my car's exhaust down a parking lot, or across a neighbor's yard, and invariably there's one or more people present to witness the event.

Anyhow, a cloud of oil smoke at startup can be normal.

However, the event should be brief and rare. If the cloud persists, if it occurs at times other than startup, if the engine runs rough, if (one 'test') with the engine idling if you can unscrew the oil tube filler cap but can't remove it against the pressure difference, the AOS is suspect. Other symptoms/signs is a sudden decrease in oil level or in some cases a CEL with error codes that indicate the DME has reached its enrichening threshold (trying to compensate for the intake air leak a failing AOS represents.)

There is always oil in the crankcase. The engine has a wet sump. What your mechanic may have been referring to is the possibility that due to the engine being on a slant -- down on one side or the other (which is an odd position for a car on a lift being worked on) -- presents an opportunity for the oil that is present on in this case the piston's crankcase surfaces, the rod, puddled on the bottom of the cylinder (most of this oil courtesy of a piston oil jet that shoots a nice stream of oil to the underside of the piston) to seep past the oil control and compression rings and into the combustion chamber.

Believe it or not this is a difficult path for the oil to follow. The piston/cylinder wall clearance is very small, the rings fit very tightly against the cylinder wall and the gaps between the rings and the piston grooves are likewise very small.

The biggest source of oil that gets burned and turned on to smoke comes from the AOS.

Many hold the belief the source of this oil comes in past the rings/pistons but it is my opinion the oil gets into the combustion chamber from having passed through (in vapor form) an AOS that simply isn't all that effective in removing this oil vapor. The oil vapor then ends up on the interior surfaces of the intake manifold and while the engine was off ran down into one or more combustion chambers. In short these engines smoke most often because the AOS sucks.

(I will go on and state that I believe that in some cases engines that exhibit higher levels of oil consumption are not oil burners in the true sense --the oil is not pulled in past worn rings/pistons, oval cylinders, worn out valve stems/guides or bad valve seals -- but simply passes through the under-performing AOS in vapor form and is routed into the engine where it its burned. In short the engine uses oil because the AOS sucks. In these cases there will be no smoking save those times some of this oil that ends up on the intake manifold's interior walls drains into the engine proper after the engine has been shut off, which I covered above.)

In your car's case, given the abnormal smoking behavior, unless you confirm the smoke was in fact water vapor, I believe the AOS in your car is bad.

But before you replace it on my say so you need to get a qualified professional's opinion, a high confidence level diagnosis.

Sincerely,

Macster.

Dirk Diggler

I am replacing my AOS tomorrow. I get smoke on startup every morning, always worse from one side or another. I have also removed the throttle body to find oil coating the inside of the inlet manifold. No smoke on acceleration or overrun when warmed up, however uses I bit of oil.

I will post my results when I'm done.

Andy

tedfromohio

I did read them but the mechanic said it looked OK and that it didn't need to be replaced. Am I wishing I had it done anyway? Probably so but have to move forward from here.

OGWGFIW

I hear ya. Feel for ya. You spent a chunk of change for piece of mind and you don't have it....yet. Hoping it's something more basic or nothing at all.

tedfromohio

Acutally, When I got the car back to the shop, the oil filler cap wasn't on the oil filler tube. It was laying down on the back of the engine.....could this have caused the smoking I was experiencing?

Barn996

I would verify oil level with your dipstick, put on the oil cap and start your car to see what it does.

San Rensho

With the car running, take the oil cap off and put your hand over the oil filler tube. You should feel the slightest, barely perceptible vacuum. If there is significant vacuum, its the aos.

Macster

I'm rather embarrassed to admit this but based on my experience, no.

Several times after changing the oil in my Boxster I have forgotten to replace the oil filler tube cap.

The only clue -- other than opening the rear trunk to put something in the rear trunk and spotting the cap laying on the carpet -- is a strange honking noise under some engine operating conditions.

Since the engine's crankcase almost always operates under pressure that is below atmospheric, this noise comes from the outside air making its way past the rubber weatherstripping that seals the fluid access bay to the underside of the rear trunk and on into the open oil filler tube.

But I have never seen any smoking at any time.

Sincerely,

Macster.

tedfromohio

Thank you!

Ted

tedfromohio

Got the car back. They adjusted the toe in and now it drives straight - much more fun. Also, no smoke. Not sure what is different now as far as that goes, but it drives great and I am having a ball.

TomF

I picked up the new AOS clamp yesterday. The parts guy had never seen them before and when I pointed out what an elegantly simple solution it was, he said, "That's pretty darn cool!" $2.21 was all it cost to save a lot of effort. Place the clamp where you want it, pull the blue clip, and voila, it clamps into place. Much easier than a standard radiator hose clamp and also much easier than the original design.