My E39 540i dash gauge for coolant temp sits at midpoint and never moves, even hot or cold. The car runs fine. Any opinion on how to troubleshoot? Any common problems with sensor or wiring or dash cluster?

Thanks for any opinion.

hmmm, check the sensor on the radiator itself, and the wiring going to it. Seems like a strange problem, and with the cooling problems of e39's, I wouldn't want to be without it!