First of all, my 2012 Focus has about 215,000 miles on it. I drive 50 miles one way to work each day on rural Interstate. Two days ago, when I left work, I was going across town to my sons house and the heater air was very cool, not warm or hot. I should also say that I am in Nebraska, and January is less than tropical. I wrote it off as the car not running long enough in cold weather. I left my sons house after midnight to head home. After driving 5 or more miles, the heater was still blowing cold air. My temperature gage was running in the normal range the whole time. Finally, I turned the temperature dial back and forth between hot and cold a few times quickly. Then all of sudden, the hot air poured out and everything seemed fine. Today, the same thing happened again. I played with the controls over and over, and finally, the hot air came. And once again, the temperature gage was in the normal range. I don't think it's the thermostat, unless it is stuck open. Could I be low on coolant? I haven't checked that.