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The fun never stops. Just spent a ton of money on getting a new oil cooler installed in my 2008 Audi A8 4.2 because oil was collecting in coolant overflow tank. After several coolant system flushes and a new overflow tank we got this problem resolved (no more sludge collecting in overflow tank). Unfortunately I noticed I was leaking coolant somewhere because I was having to top off the coolant tank every other day for about 4 days so I returned car to the independent shop that installed the oil cooler and new coolant tank. Note I could never see any leaks in the engine bay or on the ground which was mystifying me. Learned yesterday the coolant was mixing in with the oil because I noticed a couple days ago that the oil was quite black and I religiously change oil every 4K (synthetic only). After searching forum I learned that when the oil gets contaminated with coolant it can turn black. Not an expert on these cars by any means but I immediately felt the issue could be a faulty head gasket. The odd thing is the car runs perfectly, there is no white exhaust smoke and temp gauge remains at dead center after the car warms up. It has never overheated in the 5 years I've owned the car as well. The indy shop that did the oil cooler change has a good reputation, but I felt I needed to get it to an Audi specialist where it is now. I am stymied and was wondering if anyone else ever experienced this issue? By the way, car now has 185,000 miles on it but I do regular maintenance and just spent 6k in last two months on new air struts, the oil cooler and a new heater control valve. I am just about ready to give up because of the amount of money I seem to keep putting into the car.
Armchair, but I am suspicious of the diagnosis. From having done head gaskets after having them blow several times on old Audis, the oil typically turns into a milky emulsion. You often find it on the underside of the oil filler cap and/or when you look in the fill hole. Black oil is common by a few thousand miles, more so on an older motor, and is typically just accumulated blowby byproducts from normal combustion. See picture below of a decent example of the oil and water emulsion when it is actually a likely head gasket issue.
Head gaskets can blow a variety of ways--between oil and combustion chamber, between water and combustion chamber, between oil and water, or sometimes all of them I suppose. If between oil and water and you have the coolant loss, then you usually find the emulsion. If between water and combustion chamber, you expect the steam cloud (especially on a colder day) and likely the overflow bottle to bubble and eventually rupture under pressure. I haven't had oil to combustion chamber, but I would expect smoke or obvious pressure into the cankcase you would find opening the oil cap. Depending on where it blows, you most often just find one of the symptoms, not all of them. Thus emulsion in oil and no steam = the oil to combustion chamber one, and steam and not the others is the water to combustion chamber one, and so on.
If still losing coolant, as I may have posted in your prior threads IIRC, do the thorough examination. 4.2's are not known to blow head gaskets most generally, so don't jump early to that conclusion. Oil being black is not really even close to a diagnostic here, and absence of emulsion (if true)would tend to tell me you are on wrong track. Drips to ground are NOT the only diagnostic for ordinary leaks either. It can easily burn off if leaking at hot spots, in which case you look for the pink residue. See prior thread replies... It will burn off if it drips to many parts of motor, if it is leaking slowly at various parts of radiator or even at the heater valve block. I have seen all three do that. In addition the underneath covers are such it can hide the leak often, and in places like heater valve it can both hide in plenum area and also drain out in non obvious areas.
You will know immediately if coolant and oil mix. It's milky and not black. And this will form after a couple minutes with the engine running once the two mix.
Buy some dye and a uv light. It's cheap and will help you find your leak quickly.
May be the tech forgot the o-ring or it's out of the seat while pushing in the cooler pipe to the cooler and the engine. I would never believe the head gasket is the culprit. Mostly operator error.
I did find, that after doing a coolant drain and refill, I was topping off my coolant for the next few days, until it stabilized and no longer won't down. I would say, give it some time, for the coolant to distribute fully incase there is some air to be pushed out, and see if you still need to top it off... yah, i think that you would see some water droplets separating in the oil if it was getting in there. I'm not sure how black the oil is your are talking about, but usually my Mobile 1 darkens up at some point not too long after oil changes.
Last edited by Sci-fi_Wasabi; 01-07-2018 at 01:08 PM.
I think you may be over analyzing. You don’t have anything that’s symptomatic of a head gasket failure.
The coolant system on these cars can be tricky to bleed so I would suspect this as your primary issue given the works that have recently been done. Look up how to bleed the coolant system and follow that procedure and see how you get on.
If all good there and the coolant loss continues it’s obviously going somewhere so you need to really carefully check for leaks. Pin hole leaks in the radiator or around a hot part of the engine bay are hard to spot as it boils off without leaving telltale puddles. Look for crusty buildups, or as another poster suggested, UV dye to save you some time.
Okay, let me cut to the chase. Car is now at a great Audi indy shop and the bad news is they feel I need to REPLACE the engine. Engine runs great, no white exhaust smoke when driven, car has never overheated in my 4 years of ownership. Granted, I have 185k on odometer, but have serviced the car well and I'm religious about synthetic oil changes. 6K put in car in Nov' 17 (new air struts, oil cooler, heater control valve etc...).and I'm now looking at 8k for a replacement engine! Techs say they don't want to gamble sending the heads out for reworking just to find that the block may be damaged. I've owned dozens of cars and NEVER had to replace an engine so these last couple of months have really caused a great deal of dismay in Audi engineering.
I'm leaning on replacing the engine given shop has found one with about 55k on it, but knowing these cars it's inevitable that another major repair bill is looming in the next month or so. Second a8 I've owned but doubtful I can do another. This has been a very costly journey.
Take a pic of your oil and share it. Strange that it's just black and not milky. Also, for $10, buy the UV die for your coolant, black light, and yellow glasses. It's alot cheaper than $8000.
It just sounds so strange that you don't have white exhaust or milky oil. It would be a shame if it was just a cracked hose or plastic part on the intake adapter and you instead waste 8k.
01-05-2018, 04:02 AM
Coolant found in engine oil!
