Audi A6 4B V6 TDI: Overheating Issues?

Hello everyone,

I'm having a problem with my Audi A6 4B V6 TDI, engine code BAU, manufactured in 2004.
Under load, such as when driving slightly uphill on the highway at approximately 140 km/h, the coolant temperature quickly rises above 90°. When driving downhill again, the situation eases. Sustained high-speed driving is also not possible. At the same time, the oil temperature is between 100 and 110° (which is within the normal range).
Recently, I have already replaced the following parts: water pump, thermostat, radiator, and coolant temperature sensor. Unfortunately, none of these replacements have been successful.
Do you have any other ideas about what might be causing this?

Thank you in advance, and best regards.
Jan.

willem4 wrote:

... the cooling water temperature quickly rises above 90°. ...

Yes, and?
What's the problem with that?
I wouldn't worry about temperatures up to 105-110°C.
It is important to have an ACCURATE measurement of the water temperature, and not a measurement based on AI.

What was the water temperature before you replaced the parts, when they were still working correctly? Was the cooling system properly bled? Does the fan even turn on? Does the temperature sensor react quickly? What would your desired temperature be, 75°C? Can everything be programmed via OBD-2?

Bertil wrote:

willem4 wrote: ... the cooling water temperature quickly rises above 90°. ... Yes, and? What's the problem with that? I wouldn't worry about temperatures up to 105-110°C. It is important to have an ACCURATE measurement of the water temperature, and not a measurement taken via AI.

"I agree, especially if the temperature, say, on a hot day with a trailer and going uphill, exceeds 90°C. But under normal driving conditions at 140 km/h, the engine should easily handle it without much strain or overheating."

Before replacing the parts, I was already experiencing these problems. During the timing belt replacement, I also replaced the water pump and thermostat, and I thought that would solve the issue. I had previously replaced the radiator at the same time as a faulty air conditioning condenser. But, as I said, the effect remains the same.
Both the electric fan and the viscous fan are running.
It might actually be the combination instrument. I'll read the temperature from the engine control unit while driving over the next few days and then compare those values with the readings from the instrument cluster.

Dieseloptimist wrote:

What was the water temperature like before you replaced the parts, when they were still working correctly? Has the cooling system been properly bled? Does the fan even turn on? Does the temperature sensor react quickly? What would your desired temperature be, 75°C or something? Can everything be coded via OBD-2?

No, you cannot program anything via OBD-2.
@Dieseloptimist: This is now the third nonsensical "foam party" post from you this Sunday morning, is that really necessary?