I've read through quite a few posts but nothing has struck the same problem I'm having.
Just bought this car a couple months ago and everything was fine, then I had to replace my radiator because there was a hole and now I'm having problems with overheating. Started only overheating at idle but now overheats any time. Fans work fine, plenty of coolant. I did have a problem with the previous owner putting stop leak in and it clogged the heater core but I tried this thoro clean stuff and everything worked for a while but now we're back to square one. My heater when I tried blowing hot air to cool the engine a bit to get home kinda just goes between hot and cold but with no correlation to when I stop or go. What could the problem be?

 

Likely a blown headgasket, although I'm worried the stop leak may have caused a big problem as well. There are 2 of these threads on the front page. It's an extremely common problem on the 7th generation Civic.

Is your coolant reservoir filling up and your radiator seems to be draining? Upper and lower radiator hoses both getting hot after the car is fully warmed up?

Could be air in the system if it's not fully clogged with stop leak. A blown headgasket pressurizes the cooling system with hot exhaust gases, so it'll make it impossible to burp the cooling system. A heater core going in/out is one of these nice little side effects.