thats strange that truning on the AC made the car cool down as the ac doesnt cool the engine, it actually makes it work harder because it has to run an ac compressor. turning on the heat however will cool your car because the heat from the heater comes from your engine. having the heater on pushes air through the heating coil and basically helps air-cool the engine. some cars will even overheat if the heating coil is running improperly.

If it cools down when you turn the AC on, then I'd suspect a bad radiator fan or temp sensor that's not turning on the primary cooling fan

#1. When the engine is stone cold, the radiator is supposed to be filled to the top using Honda Antifreeze.

#2. When the engine is cold, the plastic coolant recovery reservoir should be 3/4 filled when the radiator pressure cap is removed.

#3 If the radiator was not filled to the top your cooling system has a leak. The dealer of your car will do an inexpensive *cooling system pressure test which will find any external or internal cooling system leaks.

If your cooling system is leaking, the coolant recovery bottle will not transfer coolant bask to the cooling system while it cools back down.

check fan

I have a 2002 Honda Civic Ex and it overheats while going down the interstate and sometimes it starts to overheat while going through town.

When we check the antifreeze it seems to be low. Its like its just disappearing.

The other day when my fiance and I tested it to see if it would still over heat we rode around and we noticed that the temperature would fluctuate and one time we noticed it just kept rising so we turned the air on and it cooled down.



Replaced:

the radiator (twice) the first one was bad but we have check this one and it is fine.

the thermostat

radiator cap

Checked:

oil (not milky)

not smoking out of the exhaust

the fans (they seem to be working properly)

any suggestions?? Car has 193,*** miles on it. Please help. I cant afford another car right now.