Are you losing any coolant? Check both the overflow tank and the radiator itself (with the engine cold of course). Blown HG's are common in 7th gen Civic's and no heat at idle+coolant coming out of the overflow are typical symptoms, along with overheating and going through coolant. It typically won't show up on a compression test either. You may not be going through much coolant, the issue is air in the system.

I would put the car on an incline, take off the radiator cap, start the car and check for bubbles.

Does the car idle funny when you first start it after sitting overnight? This is another sign.

 

I agree with droopy . I have read another case dealing with multiple changes of thermostat. My civic has been more than 4 years running without a thermostat. Temperatures here doesn't get very cold though. I would suggest removing the thermostat for the meantime to rule out a bad thermostat.

 

Just an update.. took it back to the mechanic yesterday, he claims not to have noticed any of the symptoms I told him about and suggested it may be a head gasket issue.

Now I just got to work, after about a 40 minute drive on the highway I stopped at mcdonalds. Sitting in the drive through idling, it overheated and puked some coolant outta the reservoir. I let it cool off for about 10-15 minutes, got in it to leave, and at low speeds around the parking lot/onramp it was overheating, but as soon as I hit higher speeds on the highway it cooled down to normal temp. Then I let it sit idle in the parking lot at work to see if it would overheat again... it did. WTF?

 

Overheating only while the car is sitting still is usually because the radiator fan is not working. At a moderate speed, the motion of the car will force enough air through the radiator so the fan doesn't matter.

Disconnect the fan thermal switch on the thermostat housing and put a jumper wire in the plug (on the car side). The fan should now start immediately when you turn the key on. If it does not, check fuse, motor, and relay. If the fan does start, test drive like that and confirm there is no overheating. If that solves the overheating you should replace the fan switch rather than leave it rigged to run continuously. Letting the fan run constantly is hard on the electrical system and will wear out the motor sooner.

 

I'll give the fan switch a shot when I get home from work. Would that have anything to do with the lack of heat in the cab at idle to?

 

No, heater not working at idle means the system is not full and there's a bubble of air in the top of the engine causing improper circulation, which will lead to overheating. Before you drive anywhere, take the radiator cap off (engine must be cold) and fill up the radiator all the way to the top, then start the engine with the cap off, put the heat on high, and add more to the radiator if needed.

 

So it seems like the car runs fine til air gets back in the system... any idea what could be causing that?

 

Bad head gasket.

Once you have the radiator full (and the cap still off), pull the throttle and rev up the engine. If you get bubbles and coolant coming out of the radiator, that's leakage from the head gasket.

 

try this to open the thero.
take off the rad cap, start the car till it gets warm and you see bubbles in the radiator then put it back on while running.
also if only part of the radiator is getting hot and the other is cold radiator is clogged and you should get a new one.

 

Meant to update awhile ago but got busy with the holidays. Took the car to Honda last week, they said the radiator was bad. I replaced the radiator + hoses, it was good for a few days but still overheating, however it's not puking up any coolant now.. maybe I'm just catching it before it gets to that point? I noticed the fans are not coming on... they worked when we jumped them, rad fan switch was replaced, any ideas why they aren't kicking on?