Left exhaust tips going black

[JCKST1]

I have a 2005 997 S, in December the engine was re-built this included;

All cylinders re-lined
Pistons 6, 5 & 4 replaced
All piston rings replaced
Oil fed IMS
plus a few more odd jobs

Just last week it had a new coil pack fitted.

However I have noticed the left hand side exhaust is going black on the tips, I know this is commonly due to the bore scoring but surely not after 7 months of use and even this its minimal use, probably 1500 miles. I always make sure the car is up to temp before giving it some stick and never over rev it in 1st gear.

Unfortunately the re-build was done by the previous owner (under warranty from Portiacraft) and it's only valid for him so I cant even take it back to them.

It drives fine and I haven't noticed excessive oil use however I have only had it 3-4 months now.
Should I be worrying??

[Magic919]

I'd speak to Hartech as they may well have done the work. Hopefully nothing to worry about.

[JCKST1]

I will give Portiacraft a call and see what they say, it doesn't state where the work was carried out but judging by their website they do majority of it in house as they have two Porsche trained mechanics?

[jonno_]

Have you seen any change in oil use? If it's had a decent rebuild I'd be most surprised - could it be normal carbon build-up?

To my knowledge, not many indies will do the full rebuild in-house. Most drop engine and 'box and ship it out then re-install.

[JCKST1]

I haven't noticed anything, also when it was at the Porsche specialist they gave it a good check over last week and never noticed anything.

I will get a pic of it tomorrow to show you.

[JCKST1]

Portiacraft said all the work was carried out in house and that they have never had any problems with the liners, pistons etc used on the build.

I will keep a close eye on it and hope that its normal...

[JCKST1]

Here is a couple of pics, the car was cleaned last Friday. I intentionally cleaned both exhaust tips so I could monitor them, as you can see the left side has a lot more black on it then the right. This is after approx 100-130 miles use, its my second car so when its out and warmed up it does get some stick.



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[jonno_]

Ok, thanks for posting the pics.
I think a watching brief is a good course here. Keep a note of all oil top-up amounts and mileage covered to that point.
Were the tips completely clean after the refurb?

Did they mention engine mounts? Might be the angle of the pics, though I'm surprised they didn't replace when the engine was put back in?
If you want certainty, a trip to Hartech and borescope would be c.£2-300.

Edited by jonno_ on Thursday 20th July 17:38

[JCKST1]

I will check the oil tomorrow and see whats in at the moment. I have noticed that when starting and you get the oil check gauge on the dash it varies a lot. Sometimes it can show one bar and then the following day 3/4 full?

My local Porsche specialist maybe able to borescope it. I bought the car in March/April and noticed this after about a month however it was when washing I first noticed and it's constantly coming back once cleaned off the exhaust.

[jonno_]

The oil level sensor is very sensitive to level. Might be as well to check in the same place each time.

Problematic borescore can be hard to distinguish from light marking though and the quality of equipment used and skill of user are further variables.
Your local place may be absolutely fine, just be prepared as it's sometimes not a binary thing - i.e. 100% has borescore or 100% clear.
HTH.

[Rockster]

JCKST1 said:

Here is a couple of pics, the car was cleaned last Friday. I intentionally cleaned both exhaust tips so I could monitor them, as you can see the left side has a lot more black on it then the right. This is after approx 100-130 miles use, its my second car so when its out and warmed up it does get some stick.



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Exhaust outlets look fine to me. Soot happens. For every gallon of gasoline aprox. 19lbs of carbon is produced. Most in the form of CO2 but some in the form of soot.

The engine burns way more gasoline than it does oil and it would take a huge amount of oil consumption to account for increase in soot accumulation.

Remember too there is one possibly two converters between the combustion chambers and those outlets. Thus the outlet appearance can be a reflection more on the efficiency of the converters than anything else.

Be sure you don't over fill the engine with oil. (Don't run the level low, either. I like run the oil level at the max line -- but not above! -- when the oil level is checked with the car level and the engine fully up to temperature.)

Be sure you don't run the oil too long. As the oil accumulates miles it accumulates contamination which increases the propensity of the oil to foam and create vapor. This increase in oil vapor can overwhelm the AOS (air/oil separator) and this can route a bit more oil (in the form of vapor) to the engine. If the engine/exhaust is hot no problem, but with the engine cold or not warm enough this oil can not burn as completely and the engine can generate a bit more soot. The soot can be confined to one side or the other or to one pair of outlets or the other depending up the exhaust layout.

While the AOS connects to the intake manifold at a point that should see all the vapor shared equally among cylinders in some cases when the vapor load is too heavy the oil vapor impacts the intake wall opposite the hose connection and the vapor then becomes liquid again and runs down into the engine. But in this form the liquid tends to favor one cylinder bank or even just one cylinder over the other bank or cylinders of that bank so one bank, perhaps even one cylinder, gets almost all the oil. This then means the distribution of the incomplete burning of this oil isn't shared equally between both exhaust systems since these are separate at the cylinder bank.

[Fl0pp3r]

per above, perhaps a new Air Oil Separator is worth a try if symptoms persist?

[JCKST1]

Sorry for the late reply guys, I have just seen this.

Thanks a lot for the info, really appreciated.
Here is the exhaust after another week or so, the car is still running fine but the black soot continues to build up.

Its going in for a full detail tomorrow so I will monitor it again over a couple of weeks and see if I notice any improvement.
If not what do you think the best stage of attack it?

Possible AOS sensor and oil change?


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[s4eff]

Engine rebuilt but same exhaust ? Could it be still suffering from the oil it was chucking through the exhaust prior to the rebuild ? Depending how bad the condition of the engine was of course.

[hunter 66]

Rolling road ..... bit rich in one bank ...

[JCKST1]

Thanks guys. I am hoping it is a simple solution, running rich makes sense and did cross my mind.

There is a garage local to me who do re-maps but on a proper level not these £100 job and knock things.
I might try calling them to see if I can get it on their rolling road and see what comes of it.

Is it something what could be altered electronically or is it more of a mechanical thing? sorry for the simple question!

[harleywilma]

Get rid its going to blow up ,we all know what soot means on here. Its Doooommmed I telll yeee...

[JCKST1]

harleywilma said:

Get rid its going to blow up ,we all know what soot means on here. Its Doooommmed I telll yeee...

My thoughts exactly