Had this problem for a long while now, probably since i put the civic radiator on a couple of weeks after i bought the car. I noticed the temp sensor never moved, except for when it over heated when my thermostat died, then it worked fine and shot right up to hot as it should.. But anyway, when normal driving sometimes it does this (watch the video). Really annoys me, as you can imagine. Then once the engine has settled down on the motorway or whatever it just sits on cold and literally won't budge. Like once it's has a flicker for a few minutes, it won't do it again that day. Thermostat has been changed, brand new one in there. Not losing any coolant, everything is fine. All plugs and sensors are in as far as i can see and feel. So god knows. I'm not overly bothered as will probs get a temp sensor gauge at some point.. But it's just one of those things you know. Any ideas? Video below.. (excuse the noise of the car inside, that's normal lol.. and the radio has to be turned up that loud in order to hear anything LOL)