Clouds of white smoke - headgasket

Car failed with masses of white smoke and I mean masses - C2 3.6 Tiptronic. Head gasket repaired - all ok BUT Engine management light comes on and garage suspect O2 sensors which are a �300 fix for four - no issues. However 2 genuine CATs �2900 Ouch! Is it likely just to be O2 sensors? Can they clear themselves with use? Is it likely to have taken CATs out? And my key questions - can I damage anything by trying it with faulty sensors/CATs? If put in new sensors and then find I need new CATs will trying it with old CATs have damaged new sensors? Any other suggestions? Thanks Chris

If you are getting cats efficient codes, and O2 sensor codes, you might want to drive it aggressively for a few hundred miles to see if the codes go away. But after that and they don't go away, you need to change all sensors and both cats.

More head gasket issues Wow, looks like we may have a new mode of failure

2 obvious questions based on some of the most recent failures here. Did they magnaflux the heads before reinstall as these motors do not usually blow head gaskets, they crack. Also did they check the aos to see if that was actually the issue?

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Let me get this straight. You have extreme smoking which is well known symptom linked to a failing AOS in these cars. You take it to a shop that diagnoses it as a "blown head gasket" - something that is confirmed by most respected shops to be something that never fails on these cars. Instead you give them the go-ahead for the repair and now you're getting an CEL? Then, you go back to the same shop and they point you to a complete replacement of O2 sensors and even new catalytic converters for an estimate that could exceed �4000 (including labor)??? My best advice is to run, not walk away from this shop... RUN FORREST, RUN!!!! Question, did they by chance conduct manometer reading to rule out the AOS? Is this a Porsche specialized shop? I would recommend not doing anything drastic until you get a respected shop look at it.

Take your car to someone else that knows what they are doing. These guys are bending you over the barrel.

another vote for the AOS as the likely culprit. if you (or shop) do not have a manometer, consider this DIY test: You Tube

I'd love to have a picture of that � blown headgasket" on an m96, I'd hang it on the wall next to my Unicron pic!!!!

A quote from JFP on RennTech - Let's start with the obvious: If you blew a head gasket, you are the very first one to ever do that. The multi layer steel head gaskets in these engines are stronger than the block or heads, and never fail, ever.

https://rennlist.com/forums/996-foru...own-motor.html I'm going through this right now. Get the AOS checked out!

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"Ole"? What language is that?

Many thanks for all the replies. The engine was stripped (I saw it in the stripped state) the heads were pressure tested and skimmed and all put back together. Working on the assumption that I had nothing to lose the Cats/Sensors were cleaned and the car run for a short while with Catalytic Convertor cleaner. It didn't run too badly, but not perfectly and on way to refuel the engine management light came on. Refuelled with Shell V-Power and within a mile back to normal and drove as it should. Reset the engine management light, and 500 miles later no issues. Fuel economy is as before. Took it to MOT testing station and got emissions checked - it passed with flying colours - so fingers crossed all will be OK. Like everyone here I am puzzled as to why/how the head gasket failed and so too and the Porsche Specialist who repaired the car. (Although posting on facebook when the car failed the general consensus was head gasket) They sold it to me, and have looked after it for the last two years, and have always been over reasonable when it comes to cost and charges. (including extremely reasonable with the replacement head gaskets) Once again thanks for all the comments and advice.

So where's the photo of the "failed head gasket"... My bet is that it doesn't exist (the photo or the gasket). A "general consensus on Facebook" is useless... This thread is a waste of time

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^^^^this^^^^ +1

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It's sitting on the M96 unicorn shelf next to the oil cooler that failed and that one set of tappy lifters.

Thank you for the replies which cover the two parts of my post, and for the post of the smoking due to AOS After careful consideration I decided there was little to lose by attempting to get the cats etc. cleaned, and it would appear that given no further engine management issues it has been successful - whether this is courtesy of the cleaner used, or whether it is just driving it which has done this, or a combination of both I do not know. The emissions are now fine they have been checked independently at a different local testing station and I have the printout. Will this fix last - hopefully yes but I do not know? As I am sure people will have gathered by mechanical knowledge is such that apart from the basics I do not have the necessary skills to carry out work myself, and am therefore reliant on businesses to do this. No I have not seen the blown head gasket and did not ask to see it - I did see the engine stripped down, but accept as per other posters this is an irrelevance in this situation. I also appreciate the advice regarding the head gasket and the fact that they do not fail, and that a failed one would be less likely than a unicorn - however anything can surely fail and however unlikely there must surely be a remote possibility of this happening? Maybe I am the first - I would much rather be the first who wins the Jackpot on the Lottery, and then buys another ticket and wins again - but never mind! Likewise when it comes to businesses, bad businesses can amend their ways and go good, and likewise good businesses can go bad - that's life. Having bought the car from the independent, had it serviced there, with a 6 month warranty - when the air con condensers failed after over a year, which I understand is quite a common problem, they replaced them and re-gassed the system free of charge, which they were not obliged to do. Their feedback is excellent, and they are extremely well known and highly recommended in both UK Porsche Clubs, and I am extremely well aware from 30+ years membership of another marque Club that Car Clubs can be your best friend in business, but when things go wrong they will destroy the business. . They also prior to my agreeing to strip the engine did advise me that the most likely cause of the problem is what everyone above has said, namely cracked cylinder head(s) - when stripped they advised that the head gasket had failed, but that they were also sending the heads to be pressure tested to ascertain whether they were cracked. The test showed negative hence the engine was rebuilt with new gaskets. For what its worth they too stated they were puzzled as head gaskets do not fail. So where I am at the moment is the car is fine and for that I am happy. Likewise asking around various other garages, and Porsche Club members as to what I should be paying for a head gasket repair, I have as a 'valued customer' paid well under 50% of the best figure given. Unfortunately, other than seeing the engine in bits the above will never be proven either way, and as posters have said either the garage have 'ripped me off' or been 'more than generous' - in any event they have been paid substantially less than the going rate for removing, stripping and re-building the engine. Once again thank you to everyone for their comments.

Glad your car is now fixed to your satisfaction. With the extensive amount of work, and the reasonable price, I think you will get many miles service from your car. Without a detailed parts/labor list the only thing that can be assumed is that the car is fixed.( May have gotten a new AOS in the bundle??). A proof of a failed headgasket would have been a very interesting technical information that many have falsely assumed before finally finding the real cause, and there has yet to be a "documented case/photo".