In my 91 civic dx with oem temp guage. The temp will go up to just beyond 3/4 hot then fall back to 1/2 way or just below rather quickly. It rises slowly. I just got this car and wondered if it's nromal or should I be on the look out for something? It never gets hot at an idle only when driving at 45-50 for extended periods of time or on the freeway. It never gets all the way to hot as I suppose the fan is kicking in but it is kind of a shocker to see the temp that high. Also when I use the cigarette lighter the temp guage jumps up about a 1/2 inch. Weird.
Am I just being a ninny or do these cars need the cooling system burped (bled) It was a little low when I bought it and I added some coolant and new rad cap.

 

I would suspect the thermostat. If you replace it I recommend the Honda OEM type.
However, the cigarette lighter affecting the reading might indicate a ground wiring problem. Check the connections at the themostat housing.

BTW, air in the coolant would result in an lack of or low temp reading.