Coolant Leak: Unusual Causes & Solutions

Hello everyone!

I need your advice.

'I had a problem with coolant loss after driving on the highway at full speed some time ago. I had to accept that the head gasket had unfortunately failed. After replacing it, everything was fine.'

Now, a similar problem arises:

'I can drive at 210-220 km/h (full throttle) for hours without any problems. However, if I then want to stop at a gas station and let the engine 'cool down' for a few kilometers (oil temperature then reaches 90 degrees), and then park the car at the gas station and want to drive off again after refueling, the coolant warning light comes on, and the coolant level is below the minimum mark.'
When opening the container, I don't notice any unusual pressure, which is unlike what I observed with the defective head gasket.
When I start driving again, everything is actually fine again.
What's particularly striking is that when I'm driving to Switzerland after having driven very fast in Germany, and then only drive 120 km/h in Switzerland, the coolant is gone after at most 2 kilometers. After refilling, I can then drive problem-free at 120 km/h throughout Switzerland.

I think it's becoming clear that this is somehow related to a thermal issue, but which one exactly.
I've already considered the thermostat, but why would a faulty thermostat cause the coolant to stop flowing if it's otherwise behaving normally?

By the way, I had already prepared a 'backup plan,' but after discussing the problem in more detail (see above), I ultimately decided not to go with that approach.

Here's some additional information:

The coolant reservoir cap is 2 months old.
The ZKD has a mileage of 10,000 km.
Water flosser, 1 month old.
I had the cooling system pressure tested last Friday (to 1.8 bar). The result: it's completely leak-free.

I am grateful for any suggestions.

Best regards.

mild, gentle, soft, pleasant

Hello,
'I once had a similar problem with my old diesel engine. The car would always lose coolant when the engine cooled down. There was no noticeable loss during normal operation. It turned out that a badger had left its tooth marks on the coolant hose. The bite mark was sealed by the pressure of the system, but when the engine cooled down, the pressure decreased, and the coolant leaked out through the perforated area. Quite an unusual situation, wouldn't you say?'
Regards,
Mad, the Elder.

I experienced the exact same issue with my wife's Polo.

Cold coolant = Loss! Hot coolant and pressure test = Everything OK!

Regards,

Manuel.

And what? What was the solution to the problem?

Greetings.

mild, gentle, soft, pleasant

I have a broken rubber seal on the coolant temperature sensor.

Regards,

Manuel.

Hi,

As I posted some time ago, my AXR engine also consumed a lot of coolant and emitted a burning smell. Black deposits in the expansion tank were repeatedly dismissed as "not engine oil."
Replacing the water pump didn't solve the problem. The cooling system was flushed 100 times, but the smell persisted, and the coolant kept disappearing. The expansion tank was replaced three times.
The system has been pressure-tested multiple times and found to be leak-proof!

Just before the car's transformation, the workshop desperately replaced the oil cooler (oil/water heat exchanger) ("...we had already seen a few hairline cracks in it..."). Since then, my AXR engine no longer consumes water, but now it consumes oil (0.05 liters/1000 km - which is quite reassuring). Apparently, the part was leaking. It's been quiet for 10,000 km now!

Hello!

I guess I'll check the oil cooler. I actually want to replace it with a 'real' oil cooler anyway.

Thank you.

mild, gentle, soft, pleasant

I wouldn't do that, because the radiator is, of course, also hot during the warm-up phase!

You can connect the oil cooler with a thermostat after the oil-water heat exchanger.

Regards,

Manuel.

Hello!

I was actually planning to install the oil cooler with a thermostat; I think that would be fine, right?

Greetings.

mild, gentle, soft, pleasant

If you remove the oil-water heat exchanger, you will experience noticeably longer warm-up times because the pre-warmed water in the heat exchanger heats the oil during the warm-up phase.

If he's no longer in the picture, you'll definitely notice it.

Otherwise, there's nothing against it!

Regards,

Manuel.

I think I'll try that. I'll let you know about the results.

Greetings.

mild, gentle, soft, pleasant

Hello everyone again!

I hope you can provide me with some more suggestions besides these two options. So, please don't consider this thread as closed.

Greetings.

mild, gentle, soft, pleasant

Hi Soave,

It might not be directly related to the symptoms (high pressure in the system), but have you considered the possibility of core plugs? They can sometimes be identified by hissing sounds when squeezing a coolant hose with a cold engine (with the coolant reservoir cap closed!).

Hello!

@Christian: First of all, thank you for the tip. Unfortunately, I'm not familiar with the term 'Kernlochverschüsse.' Could you perhaps give me a little more information about it?

By the way, I have some more news:

Unfortunately, I couldn't find any leaks on the oil cooler. However, on the recent trips to Switzerland, I was able to further narrow down the symptoms:

Also, ich kann problemlos 500km mit Knallgas fahren. Da läuft alles super. Wenn sich dann, wie schon erwähnt der Motor durch die langsame Fahrt (120km/h) stark abkühlt verschwindet das Wasser (das ganze Spiel beginnt bei ca. 88Grad Öltemperatur). Ok bis jetzt nicht viel neues. Aber:
Wenn ich nun auf der Rückfahrt bin, also die lange Fahrt mit 120km/h Höchstgeschwindigkeit beginne (ca 100km lang) ist alles ok, selbst wenn ich dann in Deutschland fahre und wieder Knallgas gebe ist alles i.O.. UAnd now, here it comes:
I let it idle and drive to the gas station (oil temperature 96 degrees), I turn off the engine. Then I immediately go to check what's happening with the water: Everything is fine. I fill up the gas tank and pay. Then I quickly take another look: The water is gone!

Ich habe das schon verschiedenen 'Freundlichen' so dargelegt. Everyone just said:
You have a problem!

Okay, that's it for now. Maybe you have some more ideas (I hope so).

Greetings.

soave

Okay, just to be on the safe side, I also used a new coolant reservoir cap. Of course, it didn't make any difference.

soave wrote:

Core shot hits

Hi Soave,

They are coin-sized metal closure caps. One is located in the cylinder head behind the timing belt cover (-> behind the metal plate). There is also one (or more ) in the engine block. In our Audi, they are rusted through. But your symptoms don't suggest that.

strange problem:

Where is the coolant leaking from (what is the leak location)? Or is nothing actually leaking, and is the problem due to pressure (when the container is opened, it refills, which is the opposite of what you described initially)?

That would be important to know .

Hi!

Okay, the coolant is definitely leaking. I haven't been able to pinpoint the exact source of the leak yet. It's quite difficult because the engine is very dirty due to the head gasket issue and a faulty oil line to the turbo. However, I'm having the engine cleaned right now. Hopefully, I'll be able to see some traces of where the coolant is escaping after that.
Regarding the pressure, it's as described: there's no excessive pressure when opening the container. I've experienced this before with a faulty head gasket, where there was significant pressure in the system.

Greetings.

mild, gentle, soft, pleasant