Rep Power: 0

Worked a a friend's 2004 Civic EX 1.7L VTEC today. Car overheating / no heat into passenger area / both cooling fans will come on only if AC is turned on. Main cooling fan not coming on. Changed T-stat with OEM Honda part and still temp gauge rises while car sits idling. Heater hoses into firewall one is cold other just barely warm. At first lower radiator hose was cool to touch then after car sat off not running the hose warmed up. Waterpump ?

 
Rep Power: 0

If im correct one fan should be coming on at all times (AC on or off) and the other will come on only when AC is on?

 
Rep Power: 0

Main fan will turn on when the engine FAN TEMP sensor reaches the correct operating temp. Turning on the A/C and seeing both fans shows fans are good and the relay as the AC has an override. Fan remperature switch could be in question now I think. But does not explain no heat inside cabin.

 
Rep Power: 812

bad fan temp switch and prolly bad heater control valve.

 
Rep Power: 0

Is the fan temp swtich the one coming out the left side of the T-stat housing ? And the heater control valve is the cable actuated valve on the heater hose just at the firewall before it goes in to the pass compartment area ?

 
Rep Power: 812

the ECT sensor sticks straight up above the tstat, and the fan temp is angled down below. yes for the heater valve (usually has a blue cable attached to it). have someone start the car and switch from cold to hot a few times while you watch under the hood to see if the valve lever is moving back and forth. if not, thats the problem for no heat.

 
Rep Power: 0

Had to work the air out of the system. Car now running great and STRONG heat in the cabin now. Thanks to everyone who replied.

 
Rep Power: 191

That was a temporary solution for me as well. If this happens again, your headgasket it most likely blown.

 
Rep Power: 200

The HG is usually* because something else caused an overheat. Aluminum engines vs. overheat eqauls warped head...
The fan swith may have gotten it. The fan switch being bad will make it get hot, water spews from the overflow, said water is not in the cooling system, air is and the heater is cold....

 
Rep Power: 191

^ Exactly right.

"and still temp gauge rises while car sits idling" your friend will be coming back with the same problem. I give this less than a week.

 
Rep Power: 812

for some reason, head gaskets on these cars tend to just go for no reason, usually without any previous overheating. when mine went, the temp gauge not once went above normal, and the head was not warped when they checked. many others here had similar experiences. the shop did tell me that the bottom of the head mating surface was not properly machined from the factory. it was straight, but the surface was not smooth. so maybe a defect? headgaskets should not normally go on such a small displacement engine.