I’m having a problem where the car will start getting hot when on the highway at speed. The temperature gauge goes to ¾. I can get it to cooldown by turning on the heater with the fan on high. Idling or in stop and go driving, the temperature gauge reads a little below half way. I replaced the thermostat and radiator cap. I do not seem to be loosing any anti-freeze. I bled the air out of the cooling system. The radiator fan seems to be working correctly as it goes on when the temperature rises. I’m thinking that it might be the head gasket as these are known to be problems in the Civics, but I do not see any white smoke in the exhaust or water in the oil (no milky appearance). I would have thought that the problem would be more pronounced in stop and go driving due to less air flow past the radiator. Also, has anybody used the liquid head gasket sealers and did they work ? Any help would be appreciated.