Sooty left tailpipe. Uh oh.

My new to me 2004 996 showed a sprinkling of soot on the bumper above the left exhaust after an afternoon of hard charging with a buddy. The next start-up had some black spit out of that tailpipe onto the garage floor. (The spit was tasteless, odorless and dried quickly so was probably water.) No soot or spitting on several less exuberant drives, and no other signs or symptoms including nothing from the right tailpipe. It's too soon to say anything about oil consumption. The car has 79k miles on the clock. All my reading before buying my 40 Jahre points to some bore scoring, but the PPI included a clean from-below borescoping. How screwed am I? Did the mechanic miss scoring during the PPI? Any other causes to think about. Thanks!

Tasteless? You verified this??!! Just wondering. I think this is normal, at least my 987 CS did this and never had bore scoring problems.

Cars that sit a lot collect condensation, which in turn can mix with soot in the exhaust and come out the tail pipe as sooty spit. I've had perfectly healthy cars do this. That said, I've also seen it happen on cars with compromised head gaskets (as the coolant leaks past the gasket into the cylinders), and the fact that it happens more after hard driving is a bit of a yellow flag. The 996 can also have a cracked cylinder head, which was fairly common for that motor. Condensation typically burns off and stops after hard driving, whereas gaskets and cracks get worse after hard driving. Bore score can create soot, but I'd expect it to be oily and come with other symptoms (tick/knock sound as the engine runs, dirty oil, oil consumption, etc.). Look for signs of mixing (oil in coolant and/or coolant in oil), which would point you toward gaskets/cracks, and signs of coolant or oil loss. Look inside your oil cap to see if there is any mocha sludge caused by mixing... Hopefully, it's just condensation, but worth watching closely.... https://www.callasrennsport.com/blog/th ... nder-heads

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Yes, tasteless. Or maybe a bit dirty, but not petroleum or coolant.

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A compression test would catch both a bad gasket and a cracked head, right?

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In theory, but a leak down test is probably better. The combustion pressure when the engine runs is way higher than when you just crank the starter, so sometimes leaks will only be apparent under those higher pressures. Leak down tests tend to catch more, because leaks have more time to reveal themselves, and they give more diagnostic info. But no reason not to do a compression check if that's what you have handy for now.

How old is the AOS? I was puffing and I replaced the AOS and the puffing stopped. Was the original AOS @ 60k miles. I never got soot tho, at least not appreciably. Maybe a slight imbalance. I recall from reading many Raby posts that one bank was a lead indicator of something, but I don’t recall which (driver?) and what (bore scoring or intermix).

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Thanks. I'm going to get the car thoroughly looked over, but the PPI didn't find the AOS malfunctioning. It's the right bank, cylinders 6, then 5 then 4 that get the bore scoring mostly. The stock exhausts cross over so it's the left tailpipe that gets sooty and smokes.

Any shop that knows what they are doing can quickly check the AOS with a manometer. And likewise a well trained shop will not miss bore scoring done from the sump . I would keep checking the coolant reservoir and the oil for signs of intermix. If no signs then just drive and enjoy .

I had the looked over at KellyMoss in Madison WI. #s 1 & 6 are scored, with 15% leak down on those two. Other than a few maintenance items the car is clean. My take is the the patient is ailing but with care will go many miles yet.

Frequent oil changes (4-5k miles or less) with “quality” oil (many available with strong anti-wear packages) should get you many miles of enjoyment even with some bore scoring… Good Luck