AOS narrow escape.

It has been a few weeks, but I thought I'd post this to, perhaps, help others to avoid disaster. I've had my 08 Cayman since last spring. In late November, after having the car serviced by my tech, I was driving from AZ to IA. In the early morning hours, I was just North of the OK/KS line when, as I was pulling into the service plaza, I heard the engine clatter violently. Blue smoke everywhere. (Like electronics, one should not let the blue smoke escape). I immediately shut it down - fearing total disaster. Towed the car back to AZ on a trailer and left it at the shop. I was virtually certain that the IMS or some other critical part had let go and I would have a rolling chassis or $20K bill. After $4K for car rental, towing, and careful inspection and repairs, the car is fine. No metal in the pan or filter. Compression fine. Runs perfectly. Here is what we believe happened. The AOS failed in such a way that pressure built up in the crankcase and blew out the right rear cam plug - the weakest point. It was a cheap aftermarket AOS of poor quality. Tech advises against buying any URO part. The tech hypothesizes that it took perhaps 10 miles to blow out 6 qts of oil. (There were 2.5 left when drained). There was no oil pressure warning, no CEL. I've never been more thrilled to spend $4K.

Whew. Disaster averted! Did you notice anything minor or funky at all in the few miles prior to the smoke and noise? Good job shutting off the engine immediately and getting a tow. Probably would have been way more than 4K otherwise. Also, did you get a PPI prior to purchase? Was wondering if anyone was able to identify a aftermarket AOS on inspection. Sent from my iPhone using Tapatalk

Wow Maynardg, just wow. Thanks for taking the time to post this info. All good stuff for our P9 community. Glad it was not a 20k problem. When looking at 20 grand, 4 grand looks like a drop in the bucket. For all members, maybe treating the AOS as a maintenance item (like the WP) is a way to avoid a 4k bill and maybe more. These problems seldom happen in the driveway. Which AZ shop did you use? It sounds like they do good work and having their name would be helpful. Eddie

With 2 987.1Ss in my garage, I keep a spare AOS in inventory and take it with me to DEs. Maynardg - did you notice any unusual oil consumption or smoke wks before the failure?

Could you please provide more details. What is the engine in your Cayman? How many miles? Did you or somebody else installed the URO part? How many miles since the install? Thanks for the post and the warning. These are small things leading to big disasters. Good that you avoided much more serious potential problem.

Sure. More information. Mine is a Base, so M97.20, 2.7L. Mileage was 77,621. I purchased the car at a well-respected used Porsche/Mercedes/Audi dealer in Phoenix for a fair price. No independent PII, but clean Carfax and a history of regular service and several needed repairs such as brakes, etc. Nothing record on the AOS replacement though. It was on the car when I bought it. I do not know if the AOS could be identified as URO, however, I doubt it. I am sure my tech would have raised the issue if he saw it. He is quite meticulous. He had plenty of opportunity to look as he had just replaced the water pump at 76,459 as a preventive. I noticed nothing until I pulled into the service plaza on I35 and the revs dropped so I could hear it. As one does sometimes in the early hours, I had the tunes cranked up. Yep, I shut it off and coasted on in. Timing was just dumb luck. I must live right. I live far from a dealer, in Prescott, AZ. The tech is Darren DeYoung and DeYoung Motors. We have an active Porsche group here, and he seems to be the exclusive tech used. Very knowledgeable.

I suspect many AOS failures are due to overfilling the oil. The number of failures that occur right after an oil change seems a bit much of a coincidence.

Highly unlikely, in in this case, I think. Darren has been caring for Porsches for a couple of decades. I've had vintage Mercedes for decades, and URO parts have the same reputation in Benz circles. If I had known.... Given that the AOS is a know design weak point, even original equipment, it is hard to know what system/oil interactions might contribute to their failure. BTW, the smoke was from oil on the exhaust system, not coming from the exhaust. No evidence of oil ingestion through the intake system.

That does not sound like an AOS failure, then; an AOS failure results in (generally) limited quantities of oil being sucked into the intake. It also results on a vacuum on the crankcase, not high pressure. And not a high vacuum either, just a lower than ambient pressure.

same thing happened to me on a road trip through California to Yosemite. I did a spirted drive through the petrified forrest in the middle of nowhere when my AOS let go. Same thoughts went through my head, there goes 20k! I pulled over in the most deserted road (a thrilling one up till that point). Of course no cell reception. I figured I was gonna be there awhile, i figured I could survive a week with all my camping gear and food/water in the Cayman. By absolute DUMB luck a tow truck drove through after a couple hours heading to some campsite in the petrified forrest where someone's battery died. He vowed to pick me up on the way back and get me back to "town" (consisting of a dozen buildings, a single motel and a gas station). I sat in that town for a few days with the car sitting at the gas station where they refused to work on a Porsche. Towing was in the thousands back to San Diego but I did finally get ahold of some Porsche mechanics the following Monday (Vision in OC was one of them). They had me take off teh oil cap and feel for a vacuum... I was scared to try to start the car, but did and dumped tons of smoke in that rude gas station's parking lot. Turns out there was a heavy vacuum and it was the AOS!!! A $300 service would fix it. Now I wasn't about to pay AAA 2k to tow it, so I got on craigslist for all the nearby large towns, Fresno, Bakersfield, and there is a services offered section and searched for private towers. I was somewhat shocked when my ad was answered by MANY people with HD pickups and trailers offering to tow me back to SD, I think $400+gas and 6 hours later I had a ride AND a tow. If you ever get stranded and need a tow, try craigslist, plenty of people looking to make a few bucks off the books. Lesson learned, pay the $150 and keep a spare AOS in the car on any road trip, I've been through 2 (the one that died after 20k I suspect was a URO, everyone will tell you URO parts are garbage in the Audi community too).

Glad it worked out for you. And thanks for the spare AOS tip. Possible caution here concerning whether these people carry the right (and enough) insurance in case of accidents. Another possibility is to rent a Uhaul or something like it with a car carrier in tow and drive oneself. The trick may be how to load the car, but at least small P cars are light.

Very interesting. I have a 2006 CS 3.4, and am sure that the AOS is original. It didn't get a lot of driving each year; just 2200 on average when I bought it, 4000 rev-happy miles since I bought it. Can confirm, from owning a 944, URO parts are pretty crappy. I got the Porsche OEM AOS from FCP (holy acronyms, batman) for under $110, I think. When it warms up, I will install replacement AOS, MAF, Numeric cables, painted center console. Right now, it is dumping snow. How did OP not see tons of smoke as six quarts of oil left the motor? I drove my Dad's Saab 9_5 when the turbo bearing went out, and the smoke was hazardous for miles. I felt so bad for those people behind me on the BWI Parkway. One would think that the oil would hit a hot part at some point and let you know. Thanks for sharing this story. I think $100 every ten years is a small price to pay to keep this failure prone part refreshed.

OP didn't lose the oil through the AOS, one of the plugs burst and it dumped out onto the street. His mechanic thinks a bad AOS caused the plug to fail, but I'm skeptical of that explanation. AOS isn't a wear-out item, it either works or it doesn't. There's little point in preventative replacement.

I am still baffled at the $4000 repair bill... looks like the shop realized OP was fearing the worst, and tagged on several hours of labor..