318i 2003 Wagon temperature gauge going to RED

Hi guys

Im new to this forum and I was wondering if anyone could help Fencelook

I have a 2003 318i Wagon, initially when I got it the car wouldnt start and temp gauge shot straight into the red without the car even running.
I replaced coil packs and car started right up and runs but temp gauge still in the red whether car has been driven or not.
I have rplaced the following:

Temp sensor on the head
Temp sensor on radiator hose
Thermostat
DME relay.

I have tested the following :
Sensor wires for earthing and continuity
ECU tested by 2 companies, one says its fried the other says its fine.

I had a Launch pro diagnostic machine on it and it pulled 3 codes

2850 Variable gear guide sensor
27C3 Thermal oil level sensor
278B Temperature sensor, engine coolant

I managed to find a mate with the same year and model BMW which was starting and running and we swapped my ecu to his car. Temp gauge went straight to red. I put his ECU in my car and temp gauge went straight to red.
When we put his ECU back in his car the temp gauge is now in the red.

Have I blown his ECU as well or is there something I'm missing ?

would really appreciate any assistance

dunno anymore