I have a 2004 Civic EX with 91,779 miles and have been experiencing some heating and cooling systems issues. The temperature gauge goes to overheat whenever I drive the car, when this happens the heating system will blow cold air. I had the thermastat REPLACED and I am still having the problem. The radiator never boils over or steams but the temp gauge always goes into the red when driving, and again when this happens the car's heating system will blow cold air. I haven't noticed white smoke from tail pipe... Anyone out there have any ideas, please! Thanks

Have your condenser fan relay tested. I had a similar problem & I had to have my A/C & condenser fan relays replaced. It wa less than $100.

I had the same problem with my 2004 civic, which I fixed myself. Do not go to mechanic for this little problem otherwise they will ask you to spend 100s of dollars for radiator flushing etc... open up your raditor cap when car is not hot and check if you have any fluid in radiator ( fluid in reservoir doesn't matter), if there is nothing in there then you have a very minor leak some where from pipes or some where in radiator, but my guess is in the small black pipe next to radiator cap. Buy car prestone coolant from walmart and fill up radiator with it, start your car, let it run for few minutes and see where it is leaking under hood. If you find any leak in pipes, try to tight screws or check your pipes see if you can fix the leak. If it is in radiator the it going to cost you some money .

I have an 04 ex d17a2, and radiator would be empty, yet resi tank was full to the brim with brown **** liquid
I removed the battery and took the resi tank out, just remove the top hose hookup and carefully the bottom. I took the hose's off and the fluid should have poured out the bottom but NOTHING, until I took a pipe cleaner and stuck it in the bottom valve and it all poured out so I cleaned everything and made sure the tubes, valves were
Flowing. I drained my radiator, replaced the resi tank, filled the radiator and it did the trick. One clogged tiny hole is the answer to probably so many cars and people spend hundreds. I'm just saying check it out you never know.

Check for leaks is the best. I had a $2k repair job done and still overheats. 1 hose finally broke and I replace it. It was the little bypass hose to the throttle body intake. After $2k spent . 1 cheap hose solved my overheating no more coollent lost no more overheat. I hope this helps.