Tx for your respondes. Engine water not boiling, etc, the Thermo is stock and tested, brass plate is in.
I do not trust Borletti and in combination with a new sender I got from Jäckel/Hamburg some time ago (he knew normally what he was doing)
So I am more on the trip to CALIBRATE die Borleti against the reality. So a Measure on a HOT running engine right at the exit for the sender would be for now all my desire. From there I can go backwards to find potential issue. As I Assume there is a miss match between gauge reading reality and the real temp. Someone with an infrared Temp meter could help to get reality.
As soon it gets a bit cooler over here in old Germany I will run the car and get infrared temp meter readings so we can compare.
TX for helping.
Mat