2004 Civic overheating (fan is not turning on)
 

I recently purchased a 2004 Honda Civic EX with 123k miles on it, I use it for sales calls. It has ran fine here around town but today I took it for about a 60 mile drive and it started overheating on me. I noticed that when I turned the AC off it went back to normal. Upon inspection i'm noticing that the radiator fan does not turn on when the AC is off so I made the assumption that its the ECT sensor, I disconnected the sensor and reconnected and the fan turned on. I'm replacing the sensor this week but was just wondering if there was anything else I may need to check, both fans turn on when the ac is on but I find it weird that this is the only situation where it overheats.....when both fans are running?

Re: 2004 Civic overheating (fan is not turning on)
 

Did the car overheat when you were sitting still or driving very slow? Do you have heat at idle?

Have you checked the coolant level? Let the engine cool off and check the overflow and the radiator.

Air in the system can cause the radiator fan to not come on also.

Re: 2004 Civic overheating (fan is not turning on)
 

Thank you for the response, it started happening in stop and go traffic (when I first noticed it) The AC started blowing warm, when I got home this evening I checked the overflow, no visible coolant, I added about 32 ounces of coolant before it came all the way up and then i ran it until the air bubble were gone. It was odd, everytime I turned the AC off it went right back to normal levels

Re: 2004 Civic overheating (fan is not turning on)
 

Check the radiator too! Just make sure the engine is cool before you remove the cap. The overflow is dry so the radiator is probably a bit low too, this would prevent the overflow from filling/draining as the engine temperature cycles.

If the radiator is low there is probably some air in the system. Air pockets will usually form in the heater core first with these cars, this is why I asked if you had heat at idle??

If you don't have heat at idle you need to bleed the system. This can also cause the radiator fan temp switch to not work properly.

The car runs a bit harder to run the A/C, if the coolant is low this probably put it over the edge and the engine started getting hot. If the coolant gets lower it will overheat without the A/C on. Also the computer will turn off the A/C if the engine starts to get above operating temp, this is why it started blowing warm air.

Keep an eye on the coolant over the next couple weeks and look under the car for signs of leaks. If the car is losing coolant and you have no visible leaks it may be a more serious problem...

Re: 2004 Civic overheating (fan is not turning on)
 

Anibis"The carhttp://images.intellitxt.com/ast/adTypes/icon1.png runs a bit harder to run the A/C, if the coolant is low this probably put it over the edge and the engine started getting hot. If the coolant gets lower it will overheat without the A/C on. Also the computer will turn off the A/C if the engine starts to get above operating temp, this is why it started blowing warm air.

well, my 03 civic runs harder when A/c is on, it may even shutoff when in motion or while driving. When putting on A/c and at idle, the engine seems to wanna bog down and shutoff, also it makes the car vibrate on and off (this doesn't happen always, but most of the time) and i have to shutoff a/c just to keep car running smoothly without any overload on the engine.

Have changed the A/c Fan so far & nothing else.
any suggestions.