Okay...I have read all other posts and while some are exactly what I am experiencing it is slightly different. My car will overheat after 30 plus minutes on the freeway. I can turn the heater on and it will sometimes allow the car to cool down. I have found that when I allow it to cool down I need to add more water. I am constantly adding water. Now, I have replaced the thermostat, water pump, radiator, overflow tank, hoses, and temp sensor. The fan is working as it should. Added dye to the radiator and cannot find signs of it anywhere on the engine. There are no leaks found under the car. Oil is fine. There is not a "sweet" smell or antifreeze smell coming from the exhaust. It is also not smoking from exhaust. The heater is not leaking and also checked condensation port on the heater core. Heater works great until it overheats then blows cold. This is how I know I need to add more coolant. I understand that the coolant needs to be going somewhere but I cannot find where that somewhere is. Coolant system has also been bled. Top and bottom hoses remain consistent with temperature. I am not sure if this has anything to do with it but I am getting exhaust smell through my heater vents. The other day it resembled a smell close to a Zippo lighter freshly filled and striking it a few times to light it. Otherwise, the exhaust smell smells clean.
After filling the radiator, you can see that it is recirculating just fine and you can tell when the thermostat opens up. I did have to put a small hose clamp on the overflow tube that attaches to the neck of the radiator where you fill it. I had to do that because it would come off or blow off. Since I have done that it has not come off but no change with water. Water is still going somewhere. The port on overflow has also been checked and is not clogged. I am pulling my hair out trying to figure out where the coolant is going. I know it is going somewhere but cannot find signs of it anywhere. Any ideas would be appreciated. Until I get responses giving me other ideas I will be changing my thermostat to a different OEM thermostat. I do not think that will change anything but I am out of options. Thanks in advance. It is a Honda Civic EX automatic with the 1.7.

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    Welcome to Motor Vehicle Maintenance & Repair! This is most likely a head gasket issue. I own an '03 Civic LX which had the same problem. These cars are known to have this issue. – Pᴀᴜʟsᴛᴇʀ2 Nov 18 '18 at 4:55

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