2003 325i in-line 6 2.5L engine auto trans 180K miles

2left2go

The vehicle has had the radiator,all hoses,overflow tank,thermostat recently replaced, the cars runs great and the temp gauge shows normal,all of the sudden the temp gauge shows the car is running hot but it’s not boiling over or acting as if it’s hot,I suspect a bad gauge or sensor,has any body experienced this or have any input or ideas?We have had this vehicle in a repair shop,no indication of a blown head gasket or anything else.

kyfdx

So, what does the repair shop say about it? They can't fix it?