2003 Civic overheats in traffic

I have a 2003 Civic EX with 160K miles. The car runs great but it will sometimes over heat in traffic. It does not always overheat so it so the two mechanics I have taken it too have been unable to duplicate. I have had he thermostat changed and the relay to the cooling fan. I also changed the radiator cap. Other facts.

The heater has been very slow to heat up even when letting the car run for 15 minutes in the winter. It will heat up only once on the highway. This started at about the same time as the overheating.

It has never overheated on the highway even with 100 degree weather and the AC blasting.

Turning on the air will most of the time lower the temp.

Today after traveling 30 minutes I came to a stop and it overheated(temp gage on H). I tried to turn on the heater to attempt to cool it down and it blew cold air for about 3 minutes and never warmed. I then pulled into a lot and
neither cooling fan was running. I did not have the ac on as I am thinking the fact that the heater is so slow might be a clue to the problem.

It would appear it could be something with the cooling fan but neither mechanic thought it was that as they couldn’t duplicate the problem.

Any help is greatly appreciated.

Does the electric fan come on???

First things I’d check…make sure the fan is coming on…If not then it’s either the fan itself…or the relay switch or the temperature sensor.

The fan both work but they do not always come on. The relay has been changed. Is the temperature sensor the same as the theromstat?

No, the temperature sensor is another simple gadget. It screws into the engine block. Some of them have two circuits, one for the temperature gauge (which is apparently working) and another to control the fan. Dunno about your Civic, but a bad temperature sensor could be the source of your trouble.

Does it still overheat when the fan is on???

What is happening in the coolant reservoir?

The no heat situation sounds like a coolant level problem.

Assuming no external leaks, a failed head gasket is a strong possibility.

A similar set of symptoms was happening to my '04 Civic (1.7l D17A2 SOHC) a little over a year ago. A cylinder pressure test confirmed a leaking head gasket-the only good thing was that no coolant got into the oil.

See this post for T/S procedures. http://www.ehow.com/how_5923071_troubleshoot-honda-civic-overheating.html