earossi

Started up the 2002 Boxster S this morning and heard a loud screech sound from the engine followed by billowing white smoke from the exhaust. Engine seemed to run well except for the screech and the smoke. Shut her down, and checked all fluids. No drop in coolant level and the oil does not appear to be contaminated with coolant.

The car has about 65k miles on the odo.

Any ideas on what the cause might be and how to trouble shoot it?

txhokie4life

Starter?

when then solenoid starts to fail -- it won't disengage when the flywheel spins up when the engine kicks over. Is it continuous??? -- or a short burst of noise? (starter?)

Also possible either the water pump is failing or one of the idler pulleys is giving up.

The white smoke maybe a red herring, could be something else, or some how related.

Sometimes my Boxster S will blow oil smoke upon starting -- I think my AOS is seen better days.
I would not mistake it for white however.

m

Byprodriver

Bad AOS often causes lots of white smoke at startup & screech from air getting past RMS or front crank seal.

San Rensho

OAS failure, do not drive it. The screech you hear is vacuum getting through the rear main seal which can cause severe engine damage.

earossi

OK. So, we've put the car up on jackstands and have pulled access panels trying to sort out the issues. Eventually, we will pull the AOS, and since the car has about 65k miles on it, we plan on replacing it.

So far, we have determined that there is no loss of coolant and the oil is not milky, so it looks like a worst case scenario of a blown head gasket may not be the culprit. Also pulled a spark plug from both banks and they both look fine.

The plan is to clean things up since this is the very first time we've pulled the powertrain access panels since buying the car earlier this year. Then we'll replace the AOS as mentioned above. If that solves the smoking problem but not the screeching noise issue, the next step will be to pull the poly belt and spin all the pulleys and idlers in search of a bearing that is beginning to fail.

Any comments about this approach or alternate approaches would be appreciated.

sjfehr

The screech and smoke are both classic AOS symptoms. Seriously, you can stop troubleshooting, and just replace the AOS. The screech (which can sound an awful lot like a slipping belt and be VERY LOUD) was the failed AOS pulling vacuum on the crankcase and forcing air past the crankcase seals. Don't start the car again until fix the AOS!

The M96 is a high performance engine, and tuned for highest performance at operating temperature. This means tolerances for pistons and block and other components that expand and contract are designed to be "right" at 180F, and not 70F. As the pistons are horizontal, small amounts of oil can seep past the piston seals. It's usually not an issue when the engine is shut off hot (and seals are tight), but if you shut the engine off before it reaches operating temperature, some of the oil will seep through the cold/loose seals and into the cylinders and cause a brief puff white smoke next time you start it up. If that's all you're seeing, it's normal and harmless.

When an AOS goes, it's not typically slow or subtle.

Macster

The AOS is a good candidate but it would have been good to do some further checking.

I do not know the severity of the smoking, but a bit of smoking upon startup is well, normal, and the screech might have been something else not the AOS.

A bad SAI pump or if the car is a manual a release bearing to name two things.

Or to name 3 things, perhaps a water pump.

While the water pump most often if the culprit when it is an accessory drive issue, of course any accessory drive or even an idler/tensioner roller bearing can do this.

Up to you and your mechanic what you do.

You can replace the AOS -- enough fail and at various mileages that that's a good guess if the diagnosis isn't 100% confirmed -- to make this a reasonable course of action.

A quick test -- provided the engine wasn't showing serious untoward behavior like rough running, or making scary noises (beyond the screech which of course could be drowning out the scary noises) -- would have been to remove the belt and start the cold engine to at least confirm the noise was *not* coming from an accessory drive or idler/tensioner roller bearing.

Even a quick feel of the belt might be of some value. If you detect one (the inner) edge is sharp, or both edges are sharp, this is a sign the belt is not tracking properly and this points to an accessory drive. Most often the accessory drive is the water pump.

If the belt feels ok, if you detect no play at any of the accessory drives and all the idler roller/tensioner roller bearings feel ok, then replace the AOS.

Start the engine.

What you hear or do not hear determines what you do next.

Sincerely,

Macster.

earossi

Thanks Macster. I like the logic to your thought pattern. Actually the car is my son's, who lives in Idaho. He and I have worked on P-cars for a few years (he and I), while I have been involved with the breed for about 30 years. Mostly 911's, 944's and 968's. So, the Boxster is our first "modern" Porsche with a water cooled motor. We are in the "learning curve" part of our education and have a tendency to over analyze things in order to gain the background knowledge to diagnose and work on the car.

In Idaho, there are no close indies or dealerships, for that matter, so we are kind of on our own when it comes to diagnosing issues. Once the diagnosis is confirmed, we are fairly adept at repairing things. So, please do keep pushing the information to us.

Regards,

sjfehr

If the AOS *is* the issue (and it almost certainly is, occam's razor and all), starting the engine bears a bit of risk of hydrolocking on the leaking oil. But it's certainly the easiest way to troubleshoot, and it only takes a little oil to make a LOT of smoke; if the oil level hasn't changed, the risk of hydrolock is low.

Not all AOS failures screech, but when they do, the screech shouldn't be immediate on startup like a failed bearing or whatnot, but will take maybe a half minute or so to manifest, as is takes time for vacuum pressure to build. Another symptom of AOS failure is the oil cap will be very difficult to remove due to the vacuum on it. Once you get it off, the screech should immediately stop, replaced with your oil filler sucking like a vacuum cleaner. If this happens, the extra airflow will help pull a bunch more oil into your intake and throw up a thick smokescreen, so put it right back on!

earossi

OK. I've attached a URL that captures the sound that was heard just before we experienced the billowing white smoke. Though my son characterized the noise as a screech, it sounds more like bearing noise to me; however, it does not appear to change pitch with a change in engine speed. For those of you that have heard the noise that may accompany an AOS failure, perhaps you can provide feedback to verify that the noise is AOS related. Or, offer comments that would help us troubleshoot the noise.

http://youtu.be/zYpUjLx1Spo

sjfehr

That's pretty much what my engine sounded like when the AOS failed, complete with the sound diminishing with throttle. Does it stop when you remove the oil fill cap?

earossi

Thanks. That's what I wanted to hear, since the noise really doesn't sound like air whistling across a seal. Sounds more mechanical to me. But, now that you have confirmed it, we are full steam ahead to replace the AOS.

In my early 911's it was chain tensioners and in my 968's, it was belts. Now it is AOS's! Seems like the Porsche crew always leave at least one defect in their cars. Oh, I failed to mention that we still have to deal with the ISB issue with these Boxsters. That will be our first more advanced piece of wrenching.......as soon as we get through the AOS.

Macster

The cause of the symptoms is probably the AOS. The two that have failed in my Boxster didn't make that noise but the rest of the symptoms bear a close enough resemblance to the symptoms I saw...

I'm just a bit cautious. If one says "oh yeah X is the problem" the owner might go off and fix "X" and upon testing the engine afterwards throw caution to the wind and even if "X" was a problem and needed fixing something still serious can be wrong and it may get way more seriously wrong before the driver recognizes it as he's focused on another area of the engine or the car.

I like to remind myself that I'm not a professional mechanic and while I try to always offer what I think is reasoned, thought out advice I like to always remind someone he needs to get a 2nd opinion, and ideally of course from a professional/experienced mechanic.

Absent that he needs to think about doing more diagnostics to confirm my and his suspicions.

But of course this brings with it some risk.

Have to point out that those experienced/trained mechanics have some considerable value.

One of them is they are more efficient at diagnosing problems which exposes the engine or other systems to less risk of additional or collateral damage.

Sincerely,

Macster.

earossi

Macster,

Points well taken. Which is why we were looking at other things on the car (i.le. fluid levels, spark plugs, signs of leaks, etc.). Because of the relatively low cost of the AOS, and because this device has somewhat of a reliability problem, we will replace the AOS. Once we have the old one off the car, we'll dissect it to determine if there is any visible signs of failure as we have seen in some of the photos on the internet. So, we really have a lot of information. If on a start, we experience either the oil smoke or noise that we posted a clip of, then we will shut down the motor and begin to look at other areas such as the accessory drives. Other than the smoke and simultaneous advent of noise, the car was running well at the time of the event; so, I am confident that we can start the motor for a minute or so.

sjfehr

You may still smoke for a while as all the oil in the intake works itself out, but it should be a lot less than before.

And Macster- point taken, I probably shouldn't have worded that first post quite so definitively.