I have searched quite a bit, but so far, nothing conclusive and was wondering if any here can point me in the right direction.

2002 C4S 28K miles. When I got the car, never saw it smoke upon startup. It was not until approximately two weeks ago that I turned the car on (after resting overnight) and I got a HUGE (size of a small SUV) plume of white smoke coming from the passenger side muffler only. After 10 seconds of idling, no more smoke. I did drive it like it was meant to be driven the night before.

Fast forward a few days and in some instances, again, cold startup, I have gotten white smoke, but only about the size of two shoe boxes, from the passenger side muffler. Not necessarily redlining it the night before. Once the car has warmed up, or used a couple of times during the day, no white smoke, it is just the first startup of the day that yields the white smoke.

So, my doubts are: AOS or cracked head? What exactly does an AOS failure cause? Can I use my car until it finally totally breaks down (assuming its a failing AOS)? How can I properly diagnose that it is a cracked head instead?

Thanks in advance for your replies and observations.

 

Check your coolant to ensure there's no innermix. Sounds like a AOS though or condensation. Make sure your not over filled.
Do you have oil consumption? Some Porsche blow smoke every start-up, it's the way the oil settles. If it's just a puf when starting it could be normal, but my best guess AOS.

White smoke = water
Blue smoke = oil
Black smoke = gas

 

cheap/quick test to check for bad AOS: try to remove oil filler cap while engine is running. If cap is hard to remove + car's idle gets rough while cap is off = most likely bad AOS.

 

I heard about the filler cap removal, but it is my understanding that there should always be a vacuum there, so to proper determine this, I would need some sort of special tool to accurately measure how much vacuum pressure there is.

I just turned the car on (been off for nearly 24 hours, did redline it twice 5 minutes before parking it) and no puff of anything on startup. The smoke is random, it is not every time that I turn the car on. If the car is warm, then definitely no smoke at all. On the occasion that it does smoke, it's just on initial startup after it sits for a while.

 

Take it to have it looked at a different place. Before it explodes.

 

IMHO...neither.

Porsche flat 6 engines often eject a bit of white (oil) smoke upon cold start, after sitting overnight. With the flat 6 engine any oil film in the cylinders has no place to drain out (i.e. can't drain back into the crankcase), so when you start your car you get a puff of smoke when the oil burns off.

If you had a cracked head you would get intermix--oil in water, water in oil. You can easily check for this by inspecting the condition of the coolant in the reservoir. If it's green or pink--you're fine. If it looks like a chocolate milkshake--intermix.

Most often a bad AOS results in continuous oil smoke, particularly during high RPMs. Not a small puff on startup.

If you're really worried have your mechanic check it out. From what you've told us, I think what you're seeing is normal.

 

I was late for a meeting this morning, so I did not have a chance to look for intermix, but will do so later today. I did notice that this morning, as well as yesterday morning, that no smoke came out at all. Will check for intermix later and report back.

Just find it odd that in one case, there was a huge amount of smoke, few days later, not so much, then once in a while, just a bit of smoke.

 

Just curious, did you happen to get a wiff of the smoke? What did it smell like?

 

I did. The smell was not as "sweet" as coolant, but not as "pungent" as raw fuel. It was not as if no cats were on the car either. My meeting got pushed, so I am off to check for intermix now.

 

OK, took a few minutes and went downstairs to check this out. When I turned on the car, no smoke (just like earlier this morning and yesterday morning). Observations:

1- with the car idling, I removed the oil filler cap and even before lifting, I could clearly hear a air "intake/sucking" noise. The cap was very easy to remove. The car seemed to change idle, but ever so slightly, definitely not rough idling nor want to die out. So, removing the oil cap requires not much effort and just makes noise.

2- removed the coolant cap (sucker was on TIGHT!) and looked at it. Not really sure what to make of it. Does seem a very light, even, tan/dirtygreen color, but definitely no oil residue or drops on top of the water. I know oil and water don't mix, so i would have expected to see some sort of oily film and that was definitely not there. I would assume that if there is intermix, it would at least look like when you pour gasoline on top of water (think refilling your boat and you get overspill). The color is definitely not pink, nor "vivid" green, but perhaps it is a pink/green that has not been changed in a while, thus the color seen? I don't have the service records of the vehicle (dealer has it and wont release them to me as someone else paid for those services) so I am unsure as to when it was the last time a coolant flush was done.

Like they say, a picture paints a thousand words. See below.

 

I hate to say this, but it looks like the first sign of intermix. Is it thick? And if so, it might not ba a cracked head, it could be a bad head gasget, or the cooling system.

 

Will stick my finger in it later when it's cooler. Seemed to me that it was very thin and not thick/cloudy at all.

How can I precisely determine what is going on? Unfortunately for me, the local dealer lacks trained professionals and it has been multiple instances where I have had to tell them exactly what the problem is and how to fix it. There are no other local dealers in the country, so I am stuck between a rock and a hard place, hence me asking for advice elsewhere.

Regarding cooling system, I am actually amazed as to how cold this car runs compared to my previous 3.4 C2. This one takes a good 15 minutes to reach ±176º (since my car is Euro, it is labeled as 80ºC) and this driving in stop and go traffic in 90º+ weather. Only in really extreme hot days (100º+) have I seen the needle barely pass the "0" in the 80º marker.

 

I'll look at mine when I get home. One sign of intermix is there will be a oil film on the inside of the cap, look at it. Also, for grins go to an auto parts store and get the strips to test the coolant, it should be 50/50 and perhaps the previous owner mixed it too strong or it's too old.

 

I had the same symptoms on a 2001 C4 with 55K on the clock, Did a leak down test found one cly out of spec. it had a stuck oil ring.

 

Well, I looked at mine and the coolant is yellow and clear. You know, it may be all you need is a radiator flush and new coolant. The smoke may be normal wear and tear.