996 C4: white/blue smoke on startup, burning oil

Hey everyone, hoping for a little insight. My 2002 c4 cab has 42,000 miles. I bought it in May with 40,000 miles on it, and after a thumbs up PPI from Irvine European including compression and leakdown tests, immediately had my local shop change the oil (I will probably do it myself in the future). If it's been a period of hours or days since the car was started, I get some whitish blue smoke on startup (see attached video if all goes well). It dissipates fairly quickly but I assume it is oil since I have lost 2-3 quarts in 2000 miles (I check the onboard meter at every start up, I also pull the dipstick every 5 or 10 starts). I have kept cardboard underneath the engine in the garage since I've had it, and not even a drop has shown up there. Any thoughts? AOS? Bore scoring, or would that have revealed itself in the compression and leakdown tests?

Brad: Don't see a video? Any clicking/knocking noise at either side of engine? Both exhaust pipes showing smoke? Common advise is check oil only after not run for minimum of 24 hours on flat surface. Stick is most accurate. My operators manual says no problem if not using more than one quart in 1000 miles(!). I'm sort of a noob myself, but this is stuff I have picked up from reading and learning from those more experienced.

OK, here's the video; I kept the car in the garage to keep it flat and cold before starting. It had been sitting 24 hours before I started it here. https://youtu.be/SfV9WwO86Fg

Could be valve guide oil seals, when engine is off oil is leaking down the valves into combustion chamber hence big puff of smoke on start up. Another tell tale is smoke when shifting gear , get a friend to follow you round for a few miles, if they see puffs of smoke when you shift then clear again, this is another sign of valve guide oil seals.

Brad: The flat/cold deal was to get proper oil measurements. Looks like smoke from only left(drivers) side. Maybe right side as well, hard to tell due to shadows. Does the inside of the drivers side exhaust tip look darker(sootier) than the passenger side? Do you know if car lived anywhere cold before you bought it? Did you get a chance to listen for clicks/knocks especially on the passenger side? Again, I'm no expert just asking what I've heard asked in similar circumstances and I have similar, though not as extreme, concerns as your situation may be. I.E.: some occasional smoke on start, some ticking noise and some oil consumption.

Thanks for your replies. Here's another video; looks like smoke mostly from left side, more oil soot in left exhaust tip (aftermarket exhaust from previous owner BTW). You can hear a bit of clicking in this video, and some rough idling as well which is unusual for the car. Not able to have someone follow me right now to look for smoke between gearshifts. Car spent first couple of years in NJ, then always southern California. Thoughts? https://youtu.be/8WKi3oKwFpY

Going through 2 to 3 quarts of oil in 2000 miles is certainly not normal. That is quite excessive, even if you drive it hard. Neither is that much smoke on startup. I would have suspected bore scoring, but as you mention compression and leakdown tests should reveal that. I'd suggest a bore scope to check the cylinder walls. Agree that valve guides seals could be the culprit. Sorry I don't have more to add, but I'm sure you'll soon get suggestions and opinions from some rennlisters here with much more knowledge about these engines.

Triple: Thanks. I was hoping someone with much more knowledge than I would jump in. I was hesitant to use the "liner scoring" term due to lack of intimate knowledge and I prefer to not be an uneducated alarmist! Brad: I have read the best way to check for scored liners is to pull the pan and use a boroscope to check from the bottom as the scoring is typically low in the cylinder.

Hey everyone, thanks for your thoughts. Just dropped it off at my independent shop, they suspect AOS but will also look for evidence of valve guide seal leakage. They say that a boroscope should be unnecessary since The compression and leakdown results were so good. And I will keep you guys posted.

Update: My local independent shop replaced the AOS & hoses and topped off the oil ($1050 total). This morning I still had the smoke at startup; the shop says it will probably take some days for the oil to clear and smoke to subside. They said that they don't suspect valve guide seals nor bore scoring. I'll keep you posted.

Brad: Thanks for the update. Yes, please let us know when all the smoke disappears. Mine might be getting close to AOS time as well.

Update: definitely less smoke on cold startup today, looking like the AOS was indeed the issue. Also absolutely no resistance when removing the oil filler cap while idling (there was a bit before AOS replacement).

I love a happy ending.

Update: 5 days (and 100 miles) since AOS replacement, and it seems that I still have the same smoke problem at startup. My previous update was based on 1-2 startups which seemed not to have as much smoke, but the past few days have been the same as before AOS replacement. My local shop said it may take several days to burn off any remaining oil, but 5 days? Perhaps one of those new defective AOS' I've read about? They did not suspect bore scoring nor valve guide seals; I will be bringing it back in this week.

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They didnt suspect...but did they check?

Mine kinda does this too, small amount of Smoke, especially if it's sat for a few days. I don't have any real vacuum in the oil filler tube, so believe my AOS to be "acceptable", it drives fine and does not seem to be using any great amount of oil. From what I read elsewhere this is pretty normal, really associated with the way oil collects as the cars cool down.