What could make my 03 civic ex overheat and cool down then overheat again while losing heat inside??? Already replaced radiator, water pump, thermostat.... motor

I have a 2003 Honda Civic EX as well (158k miles). At first it would overheat when idling, and then my heater started working sporadically. It would blow cold air when idling, then hot air when driving. It would also cause my car to overheat. I would turn the temp to cold and the car temp would reduce. My coolant level would also drop to next to nothing every few months, but I never saw any pooling, or leaking from the radiator. I changed the water pump, thermostat, all the belts since I was there anyway, the water sensor and the radiator cap. After all this it was asymptomatic for 4 days, then the problems persisted. I took it to the mechanic and it was diagnosed with a blown head gasket. The test for it is fairly simple and runs ~$45 (1/2hr labor charge). I would try that before changing out more parts when you don’t need to.

Your heater has apparently restricted the coolant flow....hopefully a good system back flushing will cure the problem....use a flush obtained from a parts house....I would buy the hose kit for flushing as well...good luck to you

I have a 2003 Honda Civic with 92,000 and I have a coolant leak that only occurs at night when the engine has cooled. I flushed my radiator and that helped for two days and then it started leaking again. The overflow seems to be more than full....The leak is running down the oil pan.