Overpressure in the Lupo TDI water system

Hello.
'I drive a 2000 Lupo TDI MK: AMF. Recently, the following problem has occurred. After a long highway drive of about 500 km, the coolant temperature gauge started to indicate high temperature. I checked, and the coolant was gone. The area around the reservoir was wet. I refilled it and checked it at home. It was pushing the water out of the reservoir/cap. I replaced the reservoir and cap over the weekend. I drove it, and it seemed okay (city driving). I drove on the highway again for about 5 km at approximately 140-150 km/h, and the water was gone again! It pushed the water out of the reservoir (everything was wet), and there was some pressure in the system. My first thought was a blown head gasket. I called VAG (Volkswagen Audi Group): They said they had never seen this before, and it's probably a defective oil/water cooler.' This also suggests that there were black deposits in the old container. But does the high pressure in the system fit with that? Hoping to get some tips before I waste my money.
Thank you and greetings.
Honk.

Okay, the car has 210,000 km on the odometer. Oil and... 'The timing belt has always been replaced according to schedule (every 15,000 km or 60,000 km).'

Quote:

My initial thought: head gasket failure. Called VAG: They've never seen anything like it! Probably the oil/water cooler is defective. That also explains the black deposits in the old container. But does the high pressure in the system fit with that? I hope to get some tips before I waste my money.

Your first idea is probably the most likely. If there were oil involved (which I personally highly doubt), it would have to be a significant amount, enough to contaminate the entire cooling system. The deposits in the container are also caused by soot.
Furthermore, oil ingress through the heat exchanger is not dependent on the load.

Make sure the head gasket is properly installed, and pay attention to the head itself. Sometimes, the head gaskets become embedded in the cylinder head.

Thank you. I also took it to VAG today. They made me worried about the costs . The mechanic possibly said the head was damaged. Are the heads really that sensitive? Well, I think the small 3-cylinder engine is already under a lot of stress. Has anyone had any experience with this?
Thank you and greetings.

Quote:

Are the heads really that sensitive?

The problem is that the ZKD [presumably referring to a cylinder head gasket] can become embedded in the head if the repair is delayed for too long, and since no heads are planned [presumably for replacement or availability],...

I had a similar problem with my car, except mine has twice the number of cylinders. I'm going to share my experiences, regardless of whether they might also apply to your engine.
The ultimate problem was that the cylinder head had cracks from the combustion chamber to the cooling circuit, and under load, the combustion pressure from two cylinders blew out the cooling circuit. However, these cracks could only be detected after the head was removed. If you remove the cylinder head, have it measured. I don't know the tolerances for this engine, but in my case, the maximum acceptable value was 0.1 mm, and we measured up to 0.17 mm. According to VW, the cylinder head is irreparably damaged, and they wanted to charge me €1900 for a new one. If the measurements on your cylinder head show similarly high values, you can expect to find cracks. It's worth asking a cylinder head and crankshaft grinding shop how much it costs to have a head planed; in my case, it was €45. To be a fairy tale tax, the head must be disassembled. It costs extra if you don't do it yourself.
PS: You can always plan the cylinder heads, even if VW says no. My cylinder head grinder told me that the V6 cylinder heads can be planed down to a good 0.2mm, and local VW & Audi workshops often send their cylinder heads to him for planing. So, before you let someone pressure you into buying a new one, first check with a professional to see if the device can be repaired or not.
Best regards,

I also suspect a crankshaft bearing damage. The high pressure in the cooling system is a contributing factor, as it forces the exhaust gases into the cooling circuit until the pressure relief valve opens, or a weaker point gives way first, such as a porous connection fitting on the engine.

I generally don't believe in cracks in the head, but you can't rule it out until the head has been reworked by a trusted machinist. VW doesn't plan for these issues, and other companies might quickly shave off 1/10mm without hesitation. I haven't heard of any problems related to this. So, don't let VW talk you into anything.

However, the head must be completely disassembled for this to be done. If you want to keep driving your car for years to come, it's a good idea to have new hydraulic lifters installed, as well as new valve stem seals (if they aren't always replaced at the same time). It won't make things any worse.

If you're lucky and the problem is actually quite recent (which isn't always immediately obvious), the cylinder head is still okay, and you can likely fix it with just a head gasket replacement. I've seen things like that before, but it's quite rare.

Hello!

Since I also have a 3-cylinder engine... If you're experiencing a similar problem with a TDI and would like to know how things progressed for me, please let me know.

Best regards,
Oncle.

Hello!

My oil/water heat exchanger is leaking, which is why there is oil in the coolant.
I bypassed the oil cooler by disconnecting both coolant connections and connecting them with a piece of copper tubing, and sure enough, now oil is leaking out of the water connections on the oil cooler.
Cooling water is no longer missing.
The heat exchanger is a replaceable part at VW, which suggests it frequently fails.
According to the VW service technician, the heat exchangers tend to corrode quite easily.

Okay, so ZKD is awesome, which makes me very happy.