I've got a 2002 HC with about 140k miles on it and after my last oil change (at Walmart) it has started doing this weird thing with overheating. I typically drive long distances to work (~70 miles) and after I get off the interstate and stop at a light I'll idle for a moment. The thermostat will start rising when I take off slowly and the air conditioner will turn to warm air. It will continue to do this until I reach a higher rate of speed and does this in town until I shut down the engine.

I took it to my mechanic (the best in town) and he drove it around for a while trying to get it to pop up. It didn't so in turn he couldn't figure out what was possibly wrong.

Any ideas on what might be causing this. I saw a previous post on something similar and the issue was the head gasket or whatever. That could be the case but I haven't seen any condensation or smoke. The engine shows no visible signs of overheating aside from the a/c stopping and the thermostat going up. Help HCF! Help save my Civic! :-)

 

Overheating only while sitting still sounds like the radiator fan(s) quit. This will also cause the A/C to stop working. Overheating the engine typically does not stop the A/C. Both fans should run constantly when you idle with the A/C on. So next time it happens quickly pull over and pop the hood see if the fans are running. Avoid overheating as much as possible though.

 

What's the fix if it is the fans?

 

I believe there is a fan switch that goes bad on those which is located somewhere around the e-fan wiring. It's a cheap repair.

I hate to thread jack but I have a very similar problem with the same gen car, maybe would help solve op's problem as well. I don't appear to be losing much coolant at all if maybe just a little. If I idle for an extended period of time, the temp goes up. Gunning the engine or moving seems to fix the problem. Replaced t-stat, rad cap, and check for external leaks. Nothing. Pressure tested the radiator with success. No oil in coolant or vice versa and no noticeable performance loss. I have bled the coolant as well but it appears pressure is getting in from somewhere.