Car: 2000 Honda Civic EX, 1.6L 127 hp I4, 4-Speed Automatic Overdrive,

Problem: My engine is overheating. Whenever I drive in stop-and-go traffic for 30-45+ minutes my car starts to overheat -- in cold weather, hot weather, with the air conditioner on or off, with the air vent on or off (although, I’ve noticed that driving with the air vents on the blue/cool setting will make the car overheat faster than if I dive with the ac on).

Additional Info:
The temperature gauge will almost immediately return to near-normal levels upon turning my heater on. The car doesn't overheat with freeway driving.

My timing belt was just replaced. I have no blockages in the hoses. The hoses are new. The thermostat was also just replaced. The radiator has been flushed. The coolant mixture is balanced to the correct levels and does not fluctuate when my car overheats. My oil levels do fluctuate, however: when my car overheats, the oil levels drop. I don’t have an oil leak, nor is their any sign of water mixing with my oil (i.e. a murky gray film or color on the underside of the oil filler cap) nor does my car begin to smoke or let off steam when it overheats.

The fan seems to be working (when idling, the car will heat up, but the fan will turn on when the temp gauge climbs about to the mid point -- cooling the engine back to the normal temp. However, when I drive in stop/go traffic, the temp gauge climbs to the highest point, and will only drop once I turn on the heater on full blast), but my mechanic still thinks that my fan switch may be the problem. I just had the 100k tune-up.

Knowing absolutely nothing about cars, I asked my mechanic about the possibility of a blown, cracked, or otherwise damaged head gasket (which seems to be the consensus diagnoses in other forums dealing with similar issues) -- he scoffed and said that wasn't the problem. Hopefully, he’s right. That would be a huge kick in the pants.

Anyone have any idea why my car is overheating?

Thanks.

 

check ur coolant level....if youve just had the water pump replaced, it might not have been bled properly. take the radiator cap off, top off coolan, turn the heater on full, make sure you are getting heat and then turn the heater off, and let it go through 2 thermostat cycles then, make sure its topped off and reinstall the cap...also, if thats not ur problem, you might want to do a leakdown test to see if the headgasket is at fault. might want to double check the thermostat/fan switch, but if ur fans are kicking on, thats probably not the case.

 

check your rad cap ... if ^^ doesn't work ...

 

If your fan is coming on, your fan switch is working. If your mechanic really thinks its the fan switch, take it somewhere else that really knows hondas.
Sounds to me since it takes sooo long to overheat that it might be your headgasket...Is any coolant disappearing?
If it was a faulty waterpump,thermostat,or fan switch, I think it would overheat much sooner...
Hopefully you replaced your waterpump when you just had your timing belt done.
Id also use all OEM parts. Sometimes aftermarket parts can be troublesome...
good luck

 

just incase you didnt know (you might already)... when you put your coolant in, loosen the bleed screw on the thermostat. pour your coolant in while squeezing the bottom hose to get out any air bubbles(you want to pump the coolant with your hand by repeating the squeezing) do this while someone is pouring the coolant in. or you can pour the coolant in then run the car for 10 minutes to let the water circulate, then you can go loosen the bleed screw and pour some more coolant in afterward. whats strange is your scenario almost sounds like a fan switch problem but like you said, your fan turns on.
the one mysterious thing is your fan switch seems to be turning on late. perhaps the switch has not completely died yet but is on its way out. see about buying a new fan switch since they are rather cheap and easy to install. dont forget to pick up a new radiator cap and try getting any air bubbles out that might possibly be stuck in there.

 

Because you say that your car doesn't overheat while driving it on the freeway, that would suggest a faulty cooling fan/switch/sensor.

I would replace your rad cap with a new one and see what happens. If it starts heating up again, I'd check /replace your cooling fan temp sensor/relay. Dounds like your fan may only be operating intermittently.