I have a 03 civic lx sedan with a 1.7l non vtech and no egr valve. My issue is loosing coolant with no visible leaks.

I am currently running it with no thermostat, I'm sure that dont make a difference but I dont know what else to do!
New head gasket, yes the head was taken to a shop and done correctly. New rad and rad cap and lower rad hose (was told it was leaking).
Did pressure test it holds the pressure at 15psi. Also did the test to check for exhuast entering the cooling system and there is none in the system nor entering the system.
System has been purged correctly.

The big issue is my coolant seems to be going to my overflow tank as it expands, it does not seem to be going back into the radiator though. So I am loosing coolant possibly from that and I have to add coolant every other day about a 8th of a gallon.

The car also runs perfectly!
Any help would be appreciated!

I sure hope you don't have another bad head-gasket.

You could have a small leak somewhere. Coolant is moved to the tank when warmed up, air is pulled back in through the leak when cooling. Really look over it well for any leaks.

I have. Just looked again. I just by passed the heater core I believe it may be bad. I am hoping that is the issue. But if it was a head gasket. Would that not show up on a pressure check and or puddle coolant on my piston like it did before?

Do you see how those two things are at odds with each other?

Your coolant is being displaced into and past the overflow tank.

Only 2 ways that can happen, the coolant is boiling, or a piston is pushing microbubbles of air into the water jacket each compression stroke.

if your holding pressure, your not boiling..