Signs of a milkshake (Solved)
 

I was hoping it wouldn't come to this as head gaskets are apparently a very rare problem, but my '07 A8L w/137k is showing signs. For a few years now I've been noticing a slight coolant drop in the reservoir and eventually had an oil analysis performed which indicated coolant in my oil. Ok, so without testing for a failed head gasket, I installed a new oil cooler which solved the issue for some here in the past. New oil cooler gaskets too! I picked up an old beater car before doing this repair so I could still get around in the meantime. With fresh oil and flushed cooling system I was on my way home from a 300 mile trip when I noticed the temp gauge dip to the 1/4 mark. It use to hold steady at the half mark. A search indicates this could be a bad transmission fluid cooler or such. No big deal. The car sat in my garage for almost two months (battery on charge) and when I started it up today it turned right over but idled a bit rough for a few seconds while the check engine light flashed and then went out (misfire on cyl 5). I drove to the gas station and when I got home it sat for a few hours before I removed the engine oil cap and saw slight discoloration on the cap indicating coolant.

Does a failed oil cooler pipe allow the two fluids to mix or am I just be hopeful?
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Okay, with that new information, check cylinder 5's spark plug and compare it to another one. If it looks like it has been steam cleaned compared to the other one, you have a head gasket leak into that cylinder. You can also perform a leakdown test on each cylinder if that isn't definitive.

Engine sludge when was your last oil change

I changed the oil less than 1k miles ago, I did it when I was changing the oil cooler and flushing the cooling system. This was my daily driver the past 5 years and I've always changed the oil around the 7k mile mark, never saw the oil cap like this even though I was loosing coolant very slowly. Maybe sitting for almost two months is allowing me to see this?

I'll check the plugs later today.

Maybe the car sitting for that long allowed for condensation to build up, especially if the temperature dropped from when you had initially parked it. In addition to checking the spark plugs, clean off the cap and see if it comes back.

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Checked the spark plugs in cyl 5 & 6 and this is what I found. The noticeably whiter one is from the cyl 6, didn't have time to check the others. I knew the valve cover gaskets were leaking again, I changed those less than 15k miles ago.

I'm still loosing coolant, but I now believe that is moisture on my oil cap from the car sitting for a while in cold temps. My overflow does not bubble but when I performed a chemical test the blue fluid turned green, the instructions only mention green in regards to diesel vehicles. My reservoir is considerably low so I'm confident no coolant was introduced into the tester.

Can a faulty intake manifold cause water to mix with oil? I haven't purchased a leak down tester yet, I guess I'll get one before purchasing a compression tester at this point.

On the throttle body adapter between the throttle body and the intake manifold, there are two coolant lines, one on top and one below. The nubs on this adapter become brittle over time, possibly due to heat and the coolant mix. One of mine was cracked slightly at the bottom and I never noticed a leak but was loosing a little coolant. Some have bypassed coolant passage but I ended up replacing the adapter when I had the intake off. I'd also check the bleed valves close to the air cabin filter to make sure they are completely closed.

I appreciate the reply. I already double checked the bleed valves and they are nice and dry. I thought a failed head gasket or oil cooler was the only way water and oil could mix on these cars. Your reply gives me hope as I'm starting to really doubt I have a head gasket failure. Also, I performed the 'sniff' test in my garage with the door open, maybe the exhaust fumes contaminated my test causing fluid to turn green. I had other cars blocking the driveway at the time.

I'll check the two coolant lines mentioned.

FWIW, it is very difficult to tell from your spark plugs pictures where the oil is coming from. Stepping back, those plugs have a good amount of oil on them. Some of it is long term running through the engine and baked on, while other might be either fresh from combustion or running down the plugs as you remove them.

I would get the valve cover gaskets in order, if that is an issue contributing to this. I would also look at oil consumption rate, and maybe post that. One question I have is whether what you may have is some start up condensation running through the PCV system and then in to the engine. That creates sort of a sludgy mess combined w/ oil vapor that the engine has to burn off. It is a key contributor to valve fouling on later FSI (direct injection) gas motors. If you do a lot of short distance driven cold starts, you will have more of that condensation that doesn't burn off in a single engine cycle. If you combine it with some oil burning and probably related looser tolerances to piston rings, might explain both the general look of the plugs and some amount of water in the oil. You might also check the PCV valve, and also an obscure part often called in the vernacular the suck valve, aka the vacuum suction pump. Fancy lingo for a splitter in a vacuum line going to the brake booster--either T shaped like in my D3 W12 or Y shaped like my old C5 4.2. Search for more info.