Even though I'm new, I searched around and could not find a conclusive answer to my problem.
I've got an '02 325i, with 140k miles on it. Just today, I was driving it, and the temperature gauge was creeping up, ultimately getting hot enough for the red light to come on. In the <100 feet that I kept driving in order to have a safe place to pull over, the needle went back to normal. The needle did not stay on hot for very long, making me thing that it is something other that the engine over heating.
From what I have read from searching, worst case scenario its a head gasket if the coolant/oil is milky (which I have not checked yet; engine still hot) or it is a bad thermostat.
Any other opinions on the matter?