2003 honda civic overheating at idle?

i have a 2003 honda civic lx with 229k miles on it. Last year i noticed that it started overheating at idle but cools down again when i start moving. So i replaced the radiator, timing belt, water pump, and valve cover gasket(because it was leaking oil). This seemed to solve the problem for the whole year until a month ago i noticed it started doing the same thing again. It seems to go away when i top it off with coolant then about a couple days later it starts doing the same thing til i top it off with coolant again. There are no visible leaks. So far this is what ive done to diagnose the problem with no avail.

1) pressure tested the head gasket, everything seems fine
2) radiator holds pressure when i had a pressure test performed on it
3) engine oil doesn't look milky
4) no white smoke coming out of my exhaust
5) no visible oil leaks. Overflow resevior is full

I had a trusted mechanic suggest it could be a blown head gasket.

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