2004 honda civic ex coupe overheats when the A/C is off. The radiator fan won’t spin unless the A/C Is on
When the vehicle is cold check the coolant level in the expansion reservoir and , if equipped with a radiator cap, in the radiator itself. Fill the radiator to the top and the reservoir to the “full cold” level if necessary.
Low coolant can cause the temperature sensor(s) that commands the radiator fan(s) to run to be inoperative.
If the coolant is low then leaks and/or coolant consumption need to be investigated and corrected if faults are discovered. Filling the system and properly bleeding air from the system should cause the fans to operate without the A/C being on when temperature rise calls for cooling fan operation.
Faulty fan control temperature sensors themselves can also be the culprit and the over-heating can cause coolant expulsion and also damage the cooling system.
Do not allow the vehicle to over-heat until the problem(s) are corrected. To continue to use it in this condition can cause severe damage or exacerbate any damage that has occurred.
CSA
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Hopefully the switch is the issue, however head gasket failure is very common on this engine as it gets older.
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@TXdealer is right on with the head gasket. Very common on this model/year. The engine is robust and will give you long service if you get the head gasket repaired ASAP. Overheating is an early sign of the head gasket failing.
Thank you all. I’ll try everything else first but if all else fails I’ll do the head gasket
If all else fails I wouldn’t leap right into a head gasket replacement before I pressure tested the cooling system.
I happen to own a cooling system pressure tester I’ve had for years, but some auto parts stores had loaner test kits available. I’m not sure if that’s still the case.
Be careful to stay within cooling system pressure specifications for your make/model/engine.
Sometimes pressurizing a cold system will reveal an external leak that is not evident when the system is hot.
Loss of pressure, when testing for the required time, and no external leaks would help confirm a likely compromised head gasket .
CSA
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I used a pressure kit to find a coolant leak in my 2007 Town and Country. I borrowed the kit from a nearby O’Reilly’s. Actually, they sell their loaner tools to you, and refund the purchase price when you return the tool intact and on time. They might also have a tool you can thread into a spark plug hole and then pressurize. That can help refine a diagnosis of leaking head gasket, as well as other problems like valve seat leakage.