987 AOS catastrophic failure!

Hi All, So yesterday I had the nightmare scenario where the AOS on my Cayman (69k miles) failed spectacularly at about 35mph and by the time I pulled over and turned it off, the engine was starting to make knocking sounds. It's at my local dealership now, and the verdict from the technician is that one of the cylinders was filled with oil (hydrolocked) so the engine could be toast. However, once the plugs were pulled, the tech was able to easily turn the engine by hand, so they think it's possible there's no internal damage. They can't check rods and valves without a teardown and that would be extremely expensive so they're recommending cleaning the intake and exhaust manifolds, installing a new AOS , and seeing if it will run - no guarantees though. What do you think are the chances that the engine escaped damage after something like this? I'm clinging to any hope, but I don't want to spend a bunch of money on those repairs and then be back at square one if it doesn't work. An alternative option might be for me to tow it back to my house and do those fixes myself for the cost of parts. I'm a fairly competent DIYer. Thanks for your thoughts and opinions (and if you're at 60k, please learn from my mistake and replace your AOS now!)

I had this AOS failure last fall after 4 months of ownership (huge plumes of white smoke). As I was pulling over the engine was starting to stutter so I shut it off immediately and coasted to a safe spot on the highway shoulder. Got it towed to my shop. From what I saw, I am happy I let them do the work. Ask then to do a leak down test to to check cylinder pressures. That will verify cylinder integrity. The amount of cleaning done was immense...so many little ancilleray hoses and tubes that were filled with oil. Total items replaced were AOS , air filter, MAF (damaged beyond repair). Spark plugs were fine after a cleaning which was surprising. Fingers crossed you're in good shape..but yeah some messy work is in store.

Definitely good to replace the AOS preemptively. I have one sitting on the shelf for the next time I've got the engine cover off on my 987.2 Cayman.

You know it will be tough to correctly diagnose the problem without tearing it down. It would be awesome if you did that, and taught us. Thanks!

Glad to hear your situation was salvageable - that’s encouraging. Leakdown test is a good idea, I’ll ask them. Thanks!

Is this a 987 issue only or is the 981 also have failures? Looks fairly easy to re & re.

Looks like time for a Jake Raby R series build!

Had an AOS failure at about 100K on my way to work. Had car towed to indy shop and they checked everything out. Cleaned up intake/ exhaust systems, replaced AOS and test drove car. Seemed to be good. However a few months later I started getting CEL for CAT inefficiency. Happened 1 or 2 a year. Kept resetting light without issue. Finally replaced cats/ O2 sensors and seems to have fixed the cause of CEL, which I think stemmed from AOS failure. Be thorough in inspections.

I had the AOS fail multiple times on my 2008 Cayman S . The increased crankcase vacuum sucks in the rear main seal, which needs to be replaced or the engine will leak oil. Drop the tranny, remove clutch and flywheel. Replace seal and reassemble. About $5000 at dealer over 8 years ago. Also as already pointed out, it is very common for much of the intake plumbing to be coated with oil which needs to be cleaned, plugs either need to be cleaned or replaced. I got to the point where I preemptively replaced the AOS .

[Image-only or quote-only post; no author-written text.]

Is there a recommend aftermarket AOS that will not fail in this way?

For what it's worth, I just had a similar situation with my 2008 Cayman S . The engine screeched loudly at low RPMs but silenced when I increased engine speed. I nursed it back home where the low oil pressure light finally turned on. (If it had illuminated earlier I would have had it towed.) I just got it out of the shop today -- the mechanic replaced the AOS and everything is perfect now. He said he has NEVER had to replace the engine in a Cayman. Hope your situation is similar. P.S. I don't know of any AOS that never needs replacing. I understand the AOS can be difficult but not impossible to access by DIYers. Some owners preemptively replace theirs at 6 years or 75K -- mine lasted 18 years and 100K.

Great minds think alike! I actually reached out to him a couple days ago to inquire about a Stage II engine to replace this one. Let's just say that if I win the Powerball jackpot, and it'll be at the top of my list, lol

LN Engineering sells something called " The Ultimate AOS " that may be worth considering. It's not failure proof, but it does seem to be designed to greatly reduce the consequences of a failure. https://lnengineering.com/products/...-and-upgrades-for-porsche-boxster-cayman-and-911-engines/the-uaos-ultimate-aos/

Thanks for the info - I hadn't heard about that business with the rear main seal. Seems like it would also be a good opportunity to pull the grease seal off of the IMS bearing . And yes, by all account it looks like I'm in for a major cleanup job on both the intake and the exhaust side of things.

Thanks for sharing your story and your mechanic's comment - that's good to hear! I was under 70k so I didn't think I was pushing my luck too hard, but I was wrong. I should have been more conservative and replaced it 5k miles ago. Lesson learned.

I'm hoping that running gallons of soapy water through the cats and O2 sensors will restore them, at least enough to get things working again for a while. But yes, I've heard that sometimes when oil hits those super hot components it just polymerizes and creates a coating that's pretty much impossible to remove.

Just replaced mine @61000. Started with the idle getting goofy, then just as I got home it started to make a high pitch sound. I thought it was a pully bearing but after doing a Google search, narrowed it down to the AOS . After much effort( hose clamps that you can't see ) the new part is in and the car seems to be working as it should.

I had mine fail at maybe 60k. Huge plumes of smoke by the time I noticed it. Fortunately just required a local tow and my local shop had Sunshine back in action the next morning. I had been hearing a strange whining noise since the day before. I had a similar whining noise at about 95k and took the car in pre-emptively. Shop said failure imminent and the replacement fixed the noise. What's frustrating is that there doesn't seem to be a good replacement. There's a "racing" part, but that doesn't seem to be any less prone to failure as far as I could research. During my 2 failures, which seems more than average, I was driving daily for very short distances. I only commute 5 miles to/from work and many other trips are also short. I go through batteries like mad, to the extent that I replace proactively at 4 years. And I go through tail lights as well — probably due to low voltage.

Taking the engine cover is off, but how hard is this as a proactive do-it-yourself every 5 years?

Apologies for not updating you all on my progress, I had to step away to deal with some family business but now I'm back at it. After a lot of agonizing, I finally decided to forgo having the dealer work on the car and had it towed back home, rolled it off the flatbed, and right into my garage (a surprisingly tricky maneuver, but the tow driver was a master). Now it's up on stands, and I've pulled off and cleaned the oil out of everything from the air filter box to the intake manifolds. I also dropped the sump plate and was relieved to find no debris whatsoever, and the oil filter was clean too (cut it apart). I managed to get a borescope on the connecting rod for the #3 cylinder, the one the dealer said was hydrolocked. I also scoped the intake valves and turned the engine over by hand several times and there are no obvious signs of damage - doesn't mean there isn't any of course, but I felt justified in taking a chance and I ordered the replacement parts required to see if it will run. The one thing I am scratching my head about is the best way to get the pooled oil out of the cylinders. The oil looks pretty fouled with loose carbon deposits so I'm hesitant to just crank the engine and blow it out the spark plug holes. I managed to extract some with a syringe and a length of flexible tubing, but I'd love to get more out somehow. I'm going to think about it, but In the meantime, I'll reinstall the sump plate and oil filter and get some fresh oil in there so at least I won't be cranking it dry if I do decide to go that route. I'd hate to spin a bearing or something for lack of lubrication.

Update: It’s alive!! Over the course of this week, I replaced the failed AOS along with the upper and lower vent hoses, and reinstalled all the intake parts that I’d pulled and cleaned oil out of. Yesterday I reinstalled the plugs and coil packs, and fired the car up for the first time since the catastrophe. She ran like a champ for 30 seconds or so until I had to turn her off due to the absolutely massive clouds of oil smoke blowing out of the exhaust. There’s a lot of oil in the exhaust system still, and a bit left in the cylinders too, so this was no surprise. I’d connected a dryer vent to the tailpipe and ran it out the open door of my garage, but the wind wasn’t blowing in my favor, and within 15 seconds a churning bank of smoke completely obscured the front of my house! A neighbor would have undoubtedly called the fire department if I hadn’t shut things down pretty quickly. That said, the engine sounded good, and when I pulled codes off the car afterwards, there were none indicating a misfire. So my question to you all is, should I go for a midnight drive and burn the oil out of the exhaust under the cover of darkness, or should I try to remove the exhaust system and clean it out? What are the chances of snapping off an exhaust manifold bolt in the head? Considering they’ve been in there for 20+ years, chances seem quite high, but I’d be curious to hear your opinions.

I would take it for one normal drive each day. Don't try to rev the hell out of it and "burn it out". It gets hot enough during normal use. It should not take much time at all to get her back to normal. Just my thought. Steve

What, drive my car every day? Oh no, don't make me do that!! Seriously though, thanks, I'm leaning in the same direction. If I knew I had a very good chance of removing the manifold bolts successfully, I might try - and I may end up taking my chances eventually - but I figure why not take the less risky, albeit messier approach first? Yes, it may mean that I have to replace my cats and 02 sensors sooner than if I cleaned them out now, but thinking about snapping off a manifold bolt in the head makes me break out in a cold sweat.

LN Engineering (no affiliation) sells a something they call " The Ultimate AOS " which is pretty interesting, but it is a risk for us Californians because it might not pass a visual inspection. As for your battery problem, 3-5 years is the average lifespan so 4 years is totally normal. You might consider a battery tender though - I have a CTEK and it keeps things nicely juiced up.

Update: early Sunday morning, under the cover of darkness, I took the car for her first test drive, six weeks since the AOS failed so spectacularly. Smoke billowed from the exhaust for about five minutes before starting to taper off. I went easy, keeping the rpms as low as possible until she got up to temp, and then holding at 3000 or less. No CEL, the engine sounds smooth, throttle response immediate. What a truly lovely sound that engine makes! Cruising through my neighborhood in the early morning darkness, I admit to getting a bit emotional after having spent six long weeks wondering if I’d ever hear that sound again. The effect was amplified by the fact that I hadn’t reinstalled the insulating carpet panel over the top access hatch, so the cabin was brimming with that deep growling whirr, punctuated by happy little induction noises every time I tapped the throttle. By the time I got back home 30 minutes later, there was just the slightest wisp of smoke coming from the tailpipe. I went for another drive yesterday afternoon, this time down the coast at proper highway speeds. I gently pushed her a bit higher up the rev range, to about 5k, and all was well. I’ll keep driving her every day, pushing a bit more, but at this point the smoke has completely abated and I’m feeling a growing confidence that I dodged a bullet.