Ok so as it says I've been having a overheat problem in my 01 civic. So far I have sunk $2,500.00 into her and I'm STILL having the same problem. Allow me to start with what all has been done to her.
1st I had the radiator pressure tested for leaks, radiator appeared fine but a small leak in the hoses. Replaced them, the clamps and went ahead and did the thermostat and replaced the rad cap. It did it again later on down the run and I found out my condenser fan was no longer cutting on. So I had the condenser fan replaced. She did it again so I began to fear she had a blown head gasket. I had a mechanic shop test for high carbons in the cooling system, a leak down test of the cyclinder head and compression test which she passed. So I began to figure it was the water pump. She was a little overdue for the waterpump/ timing belt maintenance so I had those and the tensioner replaced. She did it again and I brought her home and watched for the fans to cut on which they didnt so I went and replaced the fan swith that sits in the thermostat housing and now they are cutting on fine. (watched them come on 3-4) while parked idling. SHE STILL OVERHEATS, well it doesnt techniqually overheat but the gauge climbs 3 quarters of the way. I have had this car for a year and throughout the year of owning it it has never gone above halfway. For someone to tell me it is normal for the gauge just to climb like that I dont believe it for the fact it has never done it before. I stop everytime it gets 3/4 the way cause I dont want her to overheat and cause serious damage. NO ONE CAN FIGURE OUT WHAT IS WRONG PLEASE HELP

 

Is it losing coolant? The radiator should be completely full every time you check (check only with the engine cold).

Head gasket denial can run deep. But I think you have a slow leak in the head gasket causing these problems, if the coolant in the radiator is going away after every trip. Get the system as full as possible. Do this with the engine cold. Take the radiator cap off to release any pressure and replace it. Squeeze the top radiator hose, note that there is no pressure inside. Now start the engine (cold) and rev it. Squeeze the hose again-- there should still be no pressure. If you feel pressure building right away, there is a leak in the head gasket or otherwise inside the engine. Also if you take the cap off, you might see bubbles or coolant rising up, especially when you rev the engine. Normally, there will be no motion in the radiator until after the engine has warmed up and the thermostat is open.

 

Tbh the only coolant loss I can see is what is dumping out of my reservoir when it overheats. I'll definitely try the cold start hose thing you were talking about but if it was the head gasket why would it pass all those test? Even high carbon test in the coolant system

 

Another thing, when I ride with the A/C on she doesn't overheat. There was one time I managed to catch the temperature gauge going up and cut the A/C on and it cooled back down to regular temp. I checked the fans with it off and the fans were kicking on right under halfway which would lead me to believe they are wo rking fine. But if it was a headgasket or something wrong internally with the engine (she still runs great, dosent smoke, oil isn't milky) would the A/C save it that one time? Now if I try to catch it when it's already 3/4 the way it does nothing but merely slows it down. Could their be some kind of short making the fan cut on late or? I really love this car and I would like to have her fixed. Out of everything I've done even extensively reading the repair manual I can't seam to find anything I've missed.

 

does it only overheat while sitting but not while moving ??? take the rad cap off while the engine is cold start the car and turn the heat on high and turn the fan off. then watch the rad opening for air bubbles when the bubbles stop ad coolant if needed then put the cap back on.

 

It only overheats while driving. I bleed it last night, watched that very same video. Drove her like 20 miles and she didn't overheat. I had the A/C going though. Ran with the heat on for like a mile or so. Appears to be doing okay. I appreciate all the tips and info! If it does it again, I'll post about it.

 

All you are doing by turning the A/C on is bypassing the fan switch and making the fans come on right away. That suggests that the fan switch is bad. Some people have had problems with third-party replacements.

Honda Automotive Parts
I'm talking about part #16 here, which you said you replaced before but it still doesn't seem to be working. If you unplug the switch and put a test jumper in the harness side of the plug, the fans should stay on whenever the key is on.

 

if you have to continually purge the coolant then that means somewhere air is getting into the system most likely you do have a bad head gasket.