It's 16 degrees outside, I'm on my way home. I start my 9th Gen Civic, take off, and give it a few minutes to warm up as I drive. I realize it's not warming up quickly as it has done in the past. Idrive, it begins warming up. I stop at a light, it's getting cooler. I start driving, and when the light turns green, it begins warming again. I don't stop for a while and it really gets warm. I arrive home, pull in my garage, sit, and test it at idle, it's cooling again. WTF? Thermostat? Coolant? I added coolant yesterday using what I had remaining and it topped off the radiator. Anything else? Appreciate the suggestions.