Oil in Coolant: Causes, Symptoms & Repair

Hello!

A few weeks ago, I noticed that my coolant expansion tank seemed to have gotten darker. I took a closer look and found the following: Oil droplets are floating in the coolant, a white sludge has accumulated around the filler neck, and there's no smell of exhaust. I should mention that I have a bit too much oil in the engine (I was planning to ask how the automatic transmission handles that).
Otherwise, no noticeable oil consumption, no coolant consumption, no exhaust smoke (of any kind), and it starts immediately in any condition...

Okay, aside from some occasional jerking caused by a stiff injection control valve, the engine is running great! Fuel consumption is about 7.5 liters (I'm not a particularly economical driver)!


I hope one of you can give me a tip about where the oil might be coming from, or where the white sludge is coming from at the filler neck!

Engine = AAT
Approximately 165,000 km.
Audi 100
Bj. = 94

Best regards,
Andi.

Hello,

It's likely that the head gasket is about to fail.
A higher water content (indicated by a white emulsion on the oil filler cap) in the engine oil for an extended period is not a good thing...

Best regards, Rainer.

Hello Andi,

I don't want to cause any panic, but this sounds like a blown head gasket.
Can you see air bubbles in the coolant reservoir while the engine is running?

Rainer was probably faster.

First of all, thank you for the many (quick) responses!

I can't say for sure yet whether there's bubbling in the coolant, but I'll check it out today!
The white sludge is located at the coolant reservoir filler neck, while everything appears normal at the oil filler neck.

Okay, I'll let you know when I have any news!

Greetings.
Andi.

Hello,

It could also be a faulty oil/water heat exchanger; we recently had a similar issue, and everyone immediately assumed the worst.

FBonNET wrote:

Hello, It could also be a defective oil/water heat exchanger; we recently had a similar issue, and everyone immediately wanted to blame someone.

Yes, if it has one. I couldn't find one on my 1992 AAT.

Good morning!

Okay, I've checked again, and the oil filler neck is definitely completely clean (except for the oil, of course)! There are no bubbles in the coolant, even under higher load (the clutch had to work a bit, but I don't care about that!).

Could it be that, due to my occasionally sticking fuel injection start valve, I eventually had such an early fuel injection start (of course, not me ), that excessive peak pressures built up for the crankshaft seal, and somehow, somewhere, the oil was forced into the coolant circuit?

Okay, a different question: Is there anything that can be done about this difficult-to-operate injector system (I've already tried injector system cleaners several times, which provided only slight improvement)?

I'm not sure if I have an oil/water heat exchanger, but if the 1992 AAT model doesn't have one, then I probably don't either.

Wishing you a pleasant workday!
Andi.

Hello Andi,

I once had a Golf S with a naturally aspirated diesel engine, and it also had oil in the coolant.
At first, it was just a tiny drop over hundreds of kilometers, just a slight oil leak and a black ring in the container.
Then I drove to Italy and back with the fully loaded campervan.
After that, I added a good tablespoon of motor oil to the expansion tank with a single tank of fuel.
100 kilometers later, everything was covered in a black-gray oil emulsion/clumps.
The journey of suffering must have covered at least 5000 kilometers.
Okay, let's check if there are any water-oil heat exchangers installed. Otherwise, let's get the tools and miscellaneous parts ready for the head gasket replacement.

Incidentally, as unfortunately has always been the case so far , we haven't seen anything of the improved sealing.
After replacing the ZKD (cylinder head gasket), I drove the car for another 50,000 km without any further oil leaks. Unfortunately, the radiator and heater core were never properly cleaned internally from the oil residue (I tried using dish soap, etc.).
If there's a significant amount of sludge inside, the best approach would probably be to disassemble it and flush it out with gasoline. I didn't do that back then, and as a result, the engine overheated more easily when driving in the mountains with a caravan. Therefore, I wouldn't wait as long as I did before.

Best regards, Rainer.

Morning!

@ Rainer

Did the Golf used to emit white smoke before?

@ all

I went to the dealer yesterday and had them drain the excess oil.
Then, I immediately bumped the head of the mechanic against my coolant reservoir. He thought that the oil/water heat exchanger was probably broken, but of course it could also be the head gasket!

So, it turns out the AAT does have one! Apparently, there's a rectangular box next to the oil filter, and that's the heat exchanger!

So, if my car has the AAT engine, then it should also have the 92-spec AAT.

I'll get back to you when there's any news!
Andi.

Hi,

Quote:

@ Rainer Did the Golf not also emit white smoke before?

No, no white smoke. For that to happen, the coolant would really have to be "flowing" properly.

Best regards, Rainer.

Andi aus dem Ösiland wrote:

Morning! So, it turns out the AAT does have one! Apparently, there's a rectangular box next to the oil filter, and that's the heat exchanger! So, if my car has it, then it must also have the 1992 AAT. Andi

I didn't see anything on mine that looks like a WT. At least, I recognize the rectangular box of the V6.
Model updates are, of course, possible.

@Andi: If there are no coolant hoses, there can't be a water-oil heat exchanger.

Whether it exists or not can be determined through simple logic.

@ Christians

I can't confirm it yet, and it's possible that the expert was just talking nonsense!

@ Rainer

I actually thought that you wouldn't be able to see any hoses from the outside anyway, and that the oil and water would come in through some channels inside the block!

But as I said, I will check it! (I unfortunately have to do it now ).

Evening!

Regarding the oil you've found in your coolant, the most likely culprit is the oil cooler (heat exchanger).
It's located where your oil filter screws on.
And if you expand it, create a watertight water connection, and apply pressure to the other side.
If you add sugar to it and keep it in hot water, you will definitely notice the formation of air bubbles.
Something like that happens to us about 3-4 times every quarter. It's nothing new.

Best regards.

ZeroCool22 wrote:

And if you expand this, seal the water connection tightly, apply pressure to the other side, and hold it in hot water, you will definitely notice air bubble formation. Something like that happens to us about 3-4 times every quarter.

It's nothing new.
Hi,

Are only AAT engines causing problems for you, or also TDIs (if so, which specific models)?

And if you are able to say/mention it: Where did you get the experience values (from the workshop, customer service center, etc.)?