Sludge on the coolant expansion tank cover

Hi gentlemen, I'm generally reading the 993 forum as I own a 993 4S. A friend of mine asked my opinion on a problem he has on his 996 (1999)... I could not answer, and I'd like to submit this here and hope someone could help. He has a fair amount of sludge inside the expansion tank cover. The car is running fine, not smoking. And he has a quite "spirited" way of driving in the French Pyr�nn�es. This excluding the possibility of moisture due to low usage. Any idea? generally it's coolant in oil, but here it seems to be the opposite

I can't speak to the 996 specifically. But some conditions can cause oil to mix with the coolant. Head gasket is one possibility that comes to mind. Another more problematic cause could be a crack in the head somewhere. I had this happen on a 944S2, where floating oil would collect in the coolant expansion tank. We finally traced it to an unrepairable crack in the head. It appeared to seal when the engine was warmed up. But apparenlty, when turned off, as the engine cooled the crack would widen, and the vacuum caused by the cooling coolant would suck in oil that had settled in the head.

there have been NO reports of any 996 head gasket leaks - ever... that I have heard of if it is indeed oil, then the head is suspect of a crack. This has been known to happen. Naturally one would like to rule out things like accidentaly adding oil to the car in the wrong port too I would have it properly diagnosed at a shop and fixed prior to extensive driving which might make the problem worse. Heads have been repaired before with some success. noprmally the coolant goes into the oil but there have been many cases where the oil is in the coolant. I would put some weight on that being the cause and start to head that dirrection in diagnosing it further https://rennlist.com/forums/6398961-post66.html https://rennlist.com/forums/996-foru...54-bummer.html

If he has an oil/water mix in the tank, here's what it will typically look like ... http://www.youtube.com/watch?v=k_3ODNydXrw If you can't access the video file, it looks like a mocha milkshake. The car shown here is a Boxster but you'd get the same effect with a 996. Oddly the car may run well like this for a short period but it must be addressed immediately. One question regarding your post just to ensure we are not going down the wrong road on this -- you say he has sludge, "i nside the expansion tank cover ." Is the sludge just on the bottom of the "cover/cap" or is it in the tank itself?

This is normal for an oil cap as a little condensation can form and mix with the oil residue, but I've never read about that problem on a coolant cap. My boat's paper head gasket decided to blow last year, and you wouldn't believe the coffee mess it made. On this car though, the gasket is steel, harder than the aluminum. I'm going through something similar now, although I hope it's not a cracked block. I found a tiny amount of coffee in the 1-3 tube of my AOS, but no where else thus far. On a completely unrelated note, also I noticed a very strange thing today, the 1-3 intake riser has it's gasket on, but on the 4-6 side someone used RTV silicone... hmmm...... Can you post a picture?

Thanks for your answers guys. I'll wait to be at home to watch the youtube video which is blocked here at work. To answer Zurichgnome, the sludge is on the cap. My friend should send me a picture as soon as he's at home. I'll post it right away. We x fingers hoping it's not one of the heads. JP

Quotes source post: 8641860

This may not necessarily be a major problem. When the AOS starts to fail, it sucks oil up into the intake plumbing. Moisture from outside air/rain mixing with it IMHO is likely normal. As long as coffee isn't evident in the coolant or the drained oil, there's probably no leak.

I guess the big question (and one I may have assumed the answer to) is "HOW MUCH SLUDGE?"

Gosh I just saw the video! ... ...I don't know how much sludge yet... waiting for my friend pix. Thanks for your inputs, I'll keep you updated. Cheer JP