Cooling water temperature

Hello,

The car is an A6 C4 with an AHU engine, 90 horsepower, and 158,000 kilometers on the odometer.

This morning, I experienced the following problem. The temperature was approximately -14 degrees Celsius. On my way to work, which is about 75 kilometers and consists of roughly 10% country roads, 80% highway, and 10% city traffic, my temperature gauge gradually dropped from about 90 degrees to approximately 50 degrees. When I lowered the heater slightly, the temperature increased a bit. However, only moderately warm air came out of the nozzles.

'When I drove home today, everything seemed normal. The outside temperature was around -6 degrees Celsius, and my temperature gauge read 90 degrees. The climate control display on channel 51 also showed a temperature between 88 and 90 degrees.' I was able to increase the temperature, but the display didn't change.

I checked the radiator hoses, and after 75 km, the upper hose was warm while the lower hose was cold. When I squeezed the hoses, I heard a gurgling sound in the expansion tank. The water level in the surge tank is at MIN.

I couldn't find anything in the search function that matches the symptoms exactly. Could it be related to the water pump? I've read that some models have a plastic impeller in the pump. Could it perhaps be the thermostat?

Regards,
Michael.