My '91 Accord warms up normally and stays mid-range in all temperatures except when driving and the outside temperature is below freezing. When I'm driving in these colder temps, the gauge drops back to min. As soon as I stop, the temperature goes back to mid-range. Anybody have an idea what might be the problem and how to fix.

 

replace coolant temp sensor and bleed coolant system of any access air...

 

If that doesn't do it, it sounds like your thermostat is sticking open, or at least it doesn't close all the way.

 

Where is the coolant temp sensor?

 

Your problems is the thermostat. It is stuck in the open position, hence when you are idling, the temperature stays warm and when you move, the temperature drops; cooloant is always flowing. If the coolant temperature sensor was bad, your radiator fans would not come on at all, hence the car would overheat. The job of this sensor is to tell the fans when to turn on/off. Hope this helps.

 

Thermostat for sure. Stuck open.

 

Thermostat is stuck open. I had that problem last winter. Just be careful when tighting the bolts on the waterneck.