Audi A4 B6/8E: Closed Grille for Winter?

Since my TDI only reaches temperatures of around 65-70°C in city traffic during the winter, I was wondering if there's a (partially) enclosed front grille available for the B6 model.

Perhaps a version for the Nordic countries where the upper or lower part of the radiator grille is closed off.

If there's nothing else I can do, I might install an aluminum plate behind the radiator grille to generate more heat.

PS: The thermostat is working correctly, and the dual temperature sensor is also fine.

In urban driving conditions, a partially covered front will not make much of a difference. The engine rarely operates in the load range where it can generate enough heat to contribute significantly to the cooling circuit. This means you'll have the same problem as I do with my 206 HDI70, where the interior heater also extracts too much heat from the cooling circuit. Covering the lower air intake opening only helped achieve a target temperature of 80-85 degrees Celsius during highway driving. However, it's advisable to monitor the water temperature via OBD and intervene if necessary, as the deliberately fixed water thermometers in VW TDIs, which are supposed to read exactly 90 degrees, are significantly inaccurate.