My '04 Z4 is overheating. I took it to a dealer and they replaced the sensor sending unit. The car still overheats. Fans are working. Coolant is full. Any suggestions? I also realized the temperature gauge is actually more like a switch than a gauge. It jumps in increments when the car gets hot. (buffered?) anyone have experience with this? Car only has 60k on it and has been well maintained. I don't want to take a shotgun approach to the issue and start replacing a bunch of parts needlessly.