So I have a 1999 Honda Civic Lx and am having a horrible time fixing an overheating problem. I overheat when I'm idling, especially when I have my AC on. When I turn my heater on the car cools down almost instantly and when I'm driving the car doesn't get hot. I used to have a leak but after replacing a bunch of parts I dont appear to anymore. I pressure tested myself earlier and it looked good to me. So far I have replaced the radiator, the cap, all of my heater hoses, bypass hose, all hose clamps, water pump and gasket, timing belt, and the thermostat. I'm 99% its not my head gasket because my exhaust, oil, and coolant all look good and I tried a test with my radiator cap off , another test to see if fluid flew out of my cylinders, and I used an engine block test. My AC and radiators' fans relays and fuses look good and my radiator kicks on after a while (like 15 minutes or so). Any ideas? I have no idea what else to do. Thank you.

 

Jump the radiator fan switch and test drive with the fan running all the time.

 

How would one go about doing this? Like where is the switch or would I just wire it straight to the battery?

 

Google it and you will find out how to do what mk says.

 

If I ever find my camera, I'll take some pictures and write it up.

The switch is on the thermostat housing, where the lower radiator hose meets the engine, near the starter. It's the only electrical part there. Unplug it and take a short piece of bare wire and push the ends of the wire into the two square holes in the plug. The fan should now run all the time the key is on.