Cooling water leak: Why it stops and starts?

Greetings to all of you, dear community.


I'm going to go crazy.
I last posted about my coolant level decreasing, and it did indeed decrease.
I concluded that there was a faulty ZDK.
Now I feel a bit silly, because despite several test runs with V-max speeds ranging from 10 to 30 km, I can't detect any coolant loss anymore. The coolant level in the expansion tank (G3 AFN) was last about 5mm above the maximum mark (when cold). Then I had a loss of coolant down to the level between the min and max marks, and it has remained stable there for the last 2000 km, with no further consumption detectable. I wonder what's going on with my car.
(The problem with my worn-out transmission synchronizer rings seems to have resolved itself. The shifting is smooth again, even though it was barely possible before.)

I'm still anxiously waiting for the ZKD (cylinder head gasket) to fail, even though the cooling system seems to be sealed. Does anyone know about this phenomenon? Could it be that a 10-cent AFN (air fuel nitrogen) additive, when used at maximum speed on the highway, could cause the expansion tank to overflow, especially if it's already quite full?

I want to reiterate that I'm a TDI hypochondriac, and I don't want to bother anyone with trivial matters. But how do you deal with problems, and their investigation, that suddenly disappear?

Best regards,

I think that if the fluid level is above the maximum mark, the pressure increases enough to open the valve on the lid, and the excess coolant evaporates out.

ObenbeiMutti wrote:

I would like to reiterate that I am a TDI hypochondriac

.
I think that includes many (myself included) in this forum.

Hello!
I once had a similar problem with my Passat 35i. After a long search, I replaced the coolant reservoir cap, and everything was fine. There's a pressure relief valve inside that cap.
which wasn't properly sealed.

Hi,

Perhaps there was still some air in the system, which is no longer the case.
Or have you occasionally lost track of the coolant level for a while?

First of all, thank you for the answers.

@Markus

No, the water level was always stable, just below the halfway mark. I was constantly monitoring it because of a problematic cylinder head (which was slightly leaking). Only when I topped it up to 5mm above the 'Max' mark did it gradually decrease (not abruptly) with each trip (200km), until it's now back to just below the middle, but it also stays there.

@Wolfi

I was hoping to hear something like that, but it turned out to be quiet in the middle, not at Max's place.

@Otto

The valve is located on the bell itself, and I think it's okay.

@Everyone

I'm hoping that the increased maximum speed achieved through the tuning causes the water to circulate and bubble so vigorously that it's forced back out through the pressure relief valve, until a safe level is reached. However, I haven't been able to detect any water crusts or limescale deposits on the container.


Ich beobachte weiter und ängstige mich weiterhin. I am reporting.

Best regards,

So, now the truth is coming out, and everything will become clear.

Only 'excess' coolant was pushed out, which is normal.
If the pressure exceeds the maximum limit, the pressure relief valve will release pressure until the normal level is reached.

You can only read the maximum water level when the engine is hot and the radiator fan is running. In this case, the fluid throughout the entire cooling system (engine and radiator) is hot and therefore 'expanded.'

Your current and stable water level is perfectly normal.


Have a good evening and see you tomorrow.

Georg.

I'm not surprised; I could have guessed that.

[Justification mode]
I didn't find any traces of lime scale on the outside of the container, and it only decreased by a few millimeters between each highway drive. For me, it would have been more likely that the stuff would have all come out at once.
[Justification mode off]

Thank you very much, that makes things easier.

Good evening.