Our thermostat is controlled via predefined parameters. It's mentioned in the X1 Complete Vehicle documentation. Anyway here's an explanation
https://f30.bimmerpost.com/forums/sh...3&postcount=16
It is natural when you go faster the temp goes down because of the radiator getting more air for heat exchange. The most stressing situation is stop and go traffic. In fact if you are on sport mode, the ecu will command the thermostat to ensure coolant is flowing the entire system.
Back on topic. Since there are no coolant running into that area (if you do, you have major issues!), therefore coolant temps would have little impact on the longevity of these pieces. Cooling is done via engine oil. Hence fresh oil is key.