Maybe it's not the thermostat, but only the engine bay being open in the front, bottom and sides, together with the cold temperatures. Then again, I'll try to check if the radiator is warm before the coolant temperatures reach 60-70°C. If it is, then what's next is a no-brainer.
My mechanic (aka brother-in-law), who was always sceptical about aero- an ecomods, recently offered to check if he find an engine tray for me, but he couldn't find any info on it, which confirms that none were ever produced for the P106
Yesterday I (hopefully) fixed up the wiring in the OBD socket, so I shouldn't have problems with the ScanGauge.
Today I blocked half of the upper grille, and also insulated the underside of the hood with alu-coated foam (10mm thick):
The last mod is a WAI. Normally the intake air comes from just above th radiator. I disconnected the last segment so that the air now comes from behind the rad, just above the exhaust manifold.
I then had a small drive (with the family to the doctor) of about 7-8km, then back after ~15 minutes. The engine got to 78°C before returning home, but the outdoor temp was around 0°C, so relatively warm. Also, the intake air temperature was 20°C above ambient, compared to only 5°C over ambient last time I drove, not sure if this is only from the WAI and blocked grille.