My 2004 Honda Civic just overheated. What could it

I would have it tested with a gas meter to see if the head gasket is leaking, I bet it is.

Over heating the engine is a serious concern. With the hood raised you should hear the motorized fan turn on just behind the radiator as the engine requires additional cooling.. If you look in from the rear of the radiator you should see the fan blades.

This electric powered motor operates on a thermostat and when the engine temperature rises this fan should come on. I'm assuming from your description that when driving and air is flowing through the radiator as the car travels the engine is nor overheating.

Check fan motor thermostat, check fan motor and check wiring.

Wiring Diagrams related to the Honda Civic
http://www.wiringdiagrams21.com/category/automotive/honda-automotive/civic

Motor engine cooling fan only runs as engine temperature requires additional cooling.

Hi Gabriel
This could be as simple as coolant level in the radiator down a bit or (more likely) your thermostat is sticking. I've included a link that pretty much covers the reasons that engines have an overheating issue.

Hope this helps you out.
-Steve


http://asc-ind.com/cooling-system-information/common-causes-of-overheating/

car is cold and moving is OK if not moving getting hot could be thermostat stuck close or rad.is clog.

Check thermostat first. Maybe not the problem but new thermostat and housing gasket are very cheap and with this many miles it wouldn't hurt to install new one anyway. Just a little labor.

The no-hot-air-through-the-heater makes me suspect that circulation is blocked somewhere.
Renew engine thermostat.
Flush radiator and cooling system.

For car running hot and overheating issues,i suggest to you go through this help links. Click this link below and go through the troubleshooting procedure to take care of the problems :----Car runs hot? http://howtobyme.blogspot.com/2011/11/car-runs-hot-in-traffic.html
-----------All types of car overheating problems and troubleshooting?

http://technoanswers.blogspot.com/2011/11/all-types-of-car-overheating-problems.html
Car freeze overnight and started overheating while driving?http://technoanswers.blogspot.com/2012/01/car-freeze-overnight-and-started.html-----------Engine Overheats and heater blowing cold?

http://howtobyme.blogspot.com/2011/11/engine-overheats-and-heater-blowing.html

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Car overheats and Air blows hot at idle?
http://howtobyme.blogspot.com/2011/11/car-overheats-and-air-blows-hot-at-idle.html
--------overheating? http://schematicsdiagram.blogspot.com/2011/12/buick-century-overheating.html
----------Car engine Overheats and transmission starts slipping?http://schematicsdiagram.blogspot.com/2011/12/car-engine-overheats-and-transmission.html
----------This details will help.Thanks.

Many newer cars have a bleeder to allow air out of the cooling system. (usually a brass fitting or nut on the cooling lines hard pipe) This allows proper coolant level. Could be low on level check it again very thoroughly. Caution keep an eye on temperature gage till your sure of proper level. Insufficient fluid can give uneven heat performance.
Hope this helps.

UNDER THE HOOD IN A RECTANGULAR SHAPED BLACK BOX. UNDER THE COVER IS THE DIAGRAM FOR THE FUSES AND RELAYS. HOPE THIS HELPS. KEEP ME POSTED PLEASE. BEST OF LUCK. THANKS FOR USING FIX-YA

The temperature actuated switch is stuck in the ON position if the cooling fan(s) continue to operate after the engine has cooled down. Locate the defective sensor switch and replace it to eliminate the problem. This could be continuous or intermittent and either way if the switch is faulty it should be replaced.