Greetings Neil, great choice of car
The 110-120 temp that you are seeing is the cylinder head temp which will be completely different to the thermostat temp at the bottom of the engine. Your temp sensor is located at the top of the engine at rear of the head. There is only one temp sensor and it is shared by both the ECU and MFU. Your OBD tester will be seeing exactly what your ECU is seeing whilst the gauge is getting a modified output form the micro controller onboard the MFU.
A couple of questions....
If you were to hammer down your bypass and stop the car quickly when you see 110/120C with the fan running. If you where to jump out and feel the temp of the bottom rad hose going into the thermostat housing, would the hose be hot or cold, ie is the stat open or closed at that point?
By any chance do you have an aftermarket aluminum radiator fitted?
