rccman100

So I'm about 4 months into my new-to-me 2007 C4S with 65kmiles on the clock and have noticed a small amount of gray smoke on startup. I recently cleaned the exhaust tips and noticed yesterday that the left ones are sooty, right ones are still clean and shiny. What might this suggest?

99firehawk

If the car runs fine I might leave it alone.............but if your interested in pressing further step one will be to do a leak down and compression test and look for piston ring seal problems.

rccman100

Yeah, it runs like a raped ape. No performance issues.
Just wondering what problem is on the horizon and with 8 months of Porsche CPO warranty left.. what should I do. Thanks for the comments!

rccman

Farside

I have the same issue, and my 2006 c4s uses LOTS of oil (just within Porsche acceptable standards of 1.5liter per 1000km). So i assumed that oil usage is the cause of the black soot on the tips.

I took the car in to the dealer who did a test of the engine parameters and apparently all is fine - and he specifically mentioned that the black soot on the tips was not a result of the oil usage (however he could not say what it was). Weird that its just the left side.

Also no issue with the car running-does stuggle a bit to crank over when hot, turned off, and then started on immediately. Also, it stalls once in a while and then it's not a happy camper - like my old KTM 400 that did NOT like to be started after a stall. Dealer cannot find issue so i will live with it (the cable that normally causes this issue has been replaced recently).

rccman100

I am concerned about worn piston rings...but I'm surprised it would happen at 65k miles. the car was meticulously maintained (as all cars are here).

Spokane5150

Mine uses about a quart in 3,000 miles. Currious, what brand oil do you use in your car? You can have a compression test done and if there is a weak cylinder then the compression test will expose it. I doubt the dealer will do this unless they suspect something is wrong and carbon on the exhaut tips won't convince them. BTW Mine does the same thing. I cleaned my tips and they carboned up in a couple weeks. Yes, these cars hate to be restarted if they don't go through the full warm-up cycle. Mine billows out black smoke if I try to restart it a couple times (moving cars around the drive or when washing it) before it warms up. I make sure it warms up now.

pongobaz

Have the cylinders scoped. I started noticing that the left (driver's side) exhaust tip was sootier than the other side 3 years ago. As it started getting more noticeable, the oil consumption increased until it was approx 1 liter per 2000kms; still within Porsche tolerances.
Well, last year the engine suddenly lost power, CEL started flashing and felt like it was running on 5 cylinders (which it was). The dealer pulled the plugs and used a boroscope to inspect the cylinder walls. Diagnosis was that #6 was heavily scored. Remedy: expensive rebuild or new engine. I bit the bullet and worked out a deal to get a new X51 engine from Porsche.
BTW: original engine only had 102,000kms, had been serviced religiously by the dealer with oil changes every 7000-10000 kms.
If you've got a CPO warranty still in effect, INSIST that they scope the cylinders and document any abnormal wear.

jgoga

Mine does the same thing.

John

Luxter

Gents,
you can find more info on scored cylinder bores here in guide #5:

http://www.hartech.org/buyers.html

It is a long read, but well worth it in my opinion.

Pongobaz is spot on with his observations and experience.
Driver's side exhaust tips belong to the right cylinder bank, cylinders 4-6 which are more frequent culprit.
Low temp thermostat (160*F), additional 3-rd radiator for extra cooling, more robust engine oil (perhaps 5W-40 or even 10W-40) all hep the situation, unless it is already too late.
I already installed 160*F T-stat and 3-rd rad and noticed that my oil temp. does not climb much above 200*F even on a hot day and under heavy loads although my coolant temp. did not decrease at all. I also use 5W-40 oil presently and plan to transition to 10W-40 for the next oil change. I also noticed that my relatively small oil consumption using 0W-40 dropped to nil with 5W-40 oil over +6,000 km interval. Currently Motul X-Cess in the sump.
Hope that helps.
Cheers,
=L=

rccman100

thanks all! Maybe a dumb question but why would one cylinder bank be a more frequent cultprit? Seems awfully unsymmetrical for Germans

Spiffyjiff

a cheap first bet is to get your oil analyzed. blackstone takes less than a week to get back to you w results. there would most likely be evidence/elevated metals in your oil if there was a problem with piston ring seals (copper?) or scoring (aluminum?). i've gotten mine analyzed 5x so far - the last time saw a spike in lead (possible bearing issue) but without associated metals also spiking, they were hesitant to call it an issue. lo and behold, on the latest report the lead was back to normal meaning it was probably only a harmless particle streak. either way, while not a fool proof diagnosis, it can be a peace of mind (or on the flip side, could corroborate/explain other symptoms you are having).

just my $.02.

fast1

What is your oil consumption?

rccman100

hmm...I don't know my oil consumption..I've only driven it about 300 miles so far. I'm not even sure i know yet how to check. I assume that's in the data menu? will go figure it out now...

USMC_DS1

Your electronic oil gauge has bars which equate to .4 quarts/bar. Note where you're at now and see if it drops over time/mileage to determine how much it consumes. Make sure the car is level when checking. I check my oil level prior to each start up. Takes about 5 sec for it to read once I turn the key w/o starting the engine. If all looks good then I fire up the engine.

rijowysock

thats normal. means the right side of engine is burning more oil... the 997 crosses over... so left=right... i wouldn't worry unless you have more than 1L per 1k miles consumption.