Coolant Leak Audi A6 2.5 TDI:(

Hello, fellow DIY enthusiasts.

I'm having problems with my beloved [pet/car/etc.] again.

Regarding the car: Audi A6 C4, AEL 2.5 TDI engine, mileage: 206,000 kilometers.

Das Problem: Verliert bei längerer Fahrt mit hoher Geschwindigkeit Kühlwasser über das Überdruckventil des Verschlussdeckels. Sonst
No coolant leakage detected.

I suspected a blown head gasket, but: No CO/CO2 detectable in the coolant (checked twice), not even immediately after a hard drive. No oil leaks, the head gasket area is dry. No water in the oil, no...
weisser Schlamm am Einfülldeckel, kein Öl im Wasser. KA white flag.
Sometimes, when I turn it off, it gurgles as if it's boiling, but the temperature is normal, always 90°C.
What seems strange to me is the oil temperature. I think it's rising too quickly to 130°C, and then suddenly drops again at some point. Does it have an oil/water cooler? If so, where is it, and how is it controlled?

I would be grateful for any tips on troubleshooting, and I hope you can help.

Best regards, Frank.

Hello,

- Does opening the thermostat mean the radiator will also get hot? What does the coolant temperature gauge in the cockpit indicate?
- Is the coolant reservoir cap in good condition?

Laß mal den warmen Motor im Leerlauf bei offenem Kühlwasserbehälter laufen. Vorsicht Verbrühungsgefahr ! LumTake a pen, etc.
Aus dem Rücklauf oben in den Kühlwasserausgleichsbehälter darf kein Bläschen/Strahlunterbrechung kommen. AucPress the accelerator.
If you see air bubbles or the jet of water is interrupted for a short time, it's very likely that the cylinder head gasket is damaged or that the cylinder head has a crack.

Best regards, Rainer.

Hello Rainer,

I've already replaced the thermostat and the cap, and it seemed to be better for a while. The temperature gauge seems to be working normally, and it's rising.
Normally set to 90°, the radiator gets warm/hot, and the viscous fan is running.
I'm going to run your test now, and I'll get back to you.

Best regards, Frank.

I just took the test.

'I was unable to detect any bubbles or air pockets at 2000 and 3000 RPM, however, I couldn't observe the stream because the expansion tank likely has two chambers (similar to a siphon).'
But, as I said, even at higher speeds, there wasn't a single sign of a bubble.

I don't know either...

Hi,

Surely, the thin hose from the cylinder head, where the water spurts out when the engine is running, connects to the top of the expansion tank.
Not the thick hose at the bottom of the expansion tank.
If necessary, disconnect the thin hose from the container and hold it up towards the opening of the container, then you'll be able to see more.

Best regards, Rainer.

Hi Rainer,

I could have figured that out myself, I'll look into it right away.

See you then.

Hi Rainer,

It usually worked fine, without any issues, all the way up to the rev limiter.
Do you happen to know anything about oil cooling, or whether it has an oil cooler?

Best regards, Frank.

Hi,

Well, that's just great .
So, the cylinder head gasket seems to be reasonably tight, at least for now. However, if the engine overheats frequently, it will likely fail quickly .
If you still have the old coolant reservoir cap, drill a hole in it through which you can insert a tire valve.
With this device, you can pressurize your cooling system up to 0.5 bar while the engine is off, which can help you identify leaks (e.g., in the water pump?).
If the cylinder head or gasket has a crack, please check it carefully. Do not immediately turn the starter; instead, manually turn the engine or push the car to rotate it, so that nothing happens if water has been forced into the combustion chambers.

How much water do you actually lose driving 100 km at a faster speed?

Based on my gut feeling, I'd say it's likely a head gasket issue, but if nothing obvious is found, we should continue to monitor it. There's no point in tearing down the engine block just on a suspicion.

Best regards, Rainer.

Hi Rainer,

I'll also try the pressure test using the tire valve again. However, I was almost ready to partially overhaul the engine (timing belt, water pump, seals, head gasket, etc.).
In the process, I will also delve deeper into the oil circulation system.

Best regards, Frank.

Hi, I don't have any specific experience with this, but based on logic, there are only two possible causes for the high pressure (despite the overall normal temperature):
a) It releases gas under high pressure from the cylinders through the cylinder head gasket.
b) There is a local blockage in the cooling system, which results in the water starting to boil at a point where a lot of heat needs to be dissipated.
For me, the cylinder head (rather than the engine block) and the optional oil cooler are the most likely candidates.
I would first check the oil cooler and possibly inspect it before removing (or having removed) the cylinder head.

Well, I'll just keep observing the situation for now.
Oh yeah, I just checked the hose again a little while ago and looked for bubbles.
investigated, this time there was no continuous stream of water, only when changing the gas, and still no bubbles - is the water pump broken?

'Thanks in advance. Once I know what it is, I'll post it.'

madcatxyl wrote:

This time, there was no continuous stream of water, only when changing the gas

.

Well, what do you think bubbles are? They're caused by a lack of water .

Hello everyone,

meine Kühlwasserverlustprobleme sind zunächst mal erledigt. EThere were two.
Problems that apparently complemented each other in a way that resulted in this effect.
Problem 1:
The oil filter has not been changed, and this is likely the second time it hasn't been (although it always appears on the invoice ).
While I was at it, I also found the oil cooler, which is located directly below the oil filter. It's cooled by oil and coolant, but only receives oil if the filter is working correctly and the bypass isn't being used. That's why the oil temperature behaves strangely.

One more word about the trusted workshops and car dealerships:
Watch them and make sure these completely irresponsible people face the consequences, or do the job yourselves if you can. I'll make the time to do it again.

Problem 2:
'The cooling system in the area of the heat exchanger was not fully vented. I discovered the problem through a fault code from the climate control system (malfunctioning opening lift control valve). A few drops of silicone oil resolved the issue in 10 minutes. Afterward, the bubbling sound when turning off the vehicle disappeared.'

small causes big effects.

Best regards, Frank.

Hello forum!

'I drive a gasoline car myself, but I have the exact same problem. How did you completely bleed the heat exchanger? I'm experiencing the exact same symptoms, and I'm almost at my wit's end!'

Harti wrote:

Hello forum! I personally drive a gasoline car, but I have the exact same problem. How did you completely bleed the heat exchanger? I'm experiencing the exact same symptoms, and I'm almost at my wit's end!

Okay, I understand. Please provide the German text you want me to translate into English. I will only provide the translation.

Thank you.
It's good to find a forum where people are familiar with this problem. In all the other forums I've checked, this issue hasn't been reported in versions like the one I have. However, my heat exchanger doesn't have a bleed screw, and I'm not experiencing any heating problems. Another thing I've been considering is my radiator. It's tilted forward a few degrees because the engine takes up so much space in the engine bay; otherwise, the fan blade would hit the intake manifold.

'So far, I've always bled my cooling system like this: I fill it with water up to the 'Max' mark. Then I start the engine and keep adding water until the fan turns on several times. So far, everything seemed fine, but it always stopped working after the first really fast drive (which, in this case, I define as a longer period of high RPMs). Then, even the rear window gets wet, and the lid of the expansion tank lets out a lot of water. All the hoses also become very pressurized. It also takes forever to open the lid of the expansion tank, which is probably due to the decreasing boiling point. And even the next morning after such a drive, there's often still overpressure in the system, which I notice every time I open the lid to add water.'
The longer I drive fast, the more water is 'consumed'. If I drive more leisurely, the water loss also decreases. I'm at the end of my rope...

Just so you know: The vehicle is a Golf 2, manufactured in 1991, with an engine swap to a 6-cylinder engine from a Corrado. Including the radiator and so on. (Don't ban me right away, you are my last hope! )