I have a 2003 alero with a 3.4 L engine thats running hot , i have changed the thermostat ,belt ,and water pump and it still runs hot . the only time it runs cool is when the a/c is on witch makes the fans run. I do not hear the fans kick on with out the a/c on. Is there a sencor some where that could be bad or something. Or air trapped in the sysem maybe. Its a real head scratcher. Can anyone help. PLease.

 

If the temp gauge on the panel works, the coolant temp sensor is working. The fans are both supposed to run with the A/C on, do they both run?
How hot does it get without the A/C on? My fans always turned on about 2 lines above halfway on the gauge.
I'm guessing you have air in the system. Do you hear gurgling after the car is shut off? If so, you have air. Did you bleed it with the heater on?
Sometimes it takes bleeding several times over several days to work all the air out.
You may also have a bad relay. I don't remember if there is only one fan relay or not, but look in the underhood fuse block and see.