Overheating/heater blowing cold air
 

My heater is blowing only cold or room temperature air. My heater core is not blocked and my valve is working correctly. My car over heats every time i turned my heater on.

My mechanic just bled my coolant system and said that my heater is working great now and its not over heating. Is it possible that somethign that small could cause the over heating???

I just want to make sure that theres nothing else wrong.

Yes, the system needs to be completely full (no pockets of air) to work properly. For the next few days open the radiator cap before you start (engine cold) and make sure it's staying completely full.

Having a similar problem
 

I recently bought a 2004 Honda Civic, I have only had it for about three weeks. At first the heat would get hot while I was driving, then I noticed when I would stop at a red light or idle it would get cool, so I added some anitfreeze that worked for a little bit, then it stated doing it again so I stared pushing the recirculation button heat worked fine for two days air worked really good. This morning I go out and let it warm up when I got in the car, the temp gage started going up it did not over heat but got warmer than usual turned the heat full blast it went down but the heat never would get warm. Tonight let it set and run for twenty mins still no heat but the temp gage started climbing again but did not overheat turned the ac on full blast temp gage went back down and I got it home. Over flow take is full couldn't really tell much about the radiator but still have no heat what so ever... This is the first Civic I have owned I have had three Accords and never had any problems like this HELP ME please:o

Cross posting your question, especially on post that are over 6 years old is not ideally the best way to get attention to your problem.

The easiest way I found to determine if I have enough radiator fluid in my Honda is to check it when it is cold. But the bottom line is if you have to keep adding fluid to your radiator then you have a leak somewhere. If you are not leaking radiator fluid then water flow is possibly your problem and the water pump is getting ready to go, if it has not gone bad already. I have had bad radiators, hoses, radiator caps, water pump, heater core, and even leaky water sending units.

Do you have radiator water puddling up on the ground when you are sitting just letting it idle? Just trying to help you isolate your problem, but when I recently had to change both the water pump and the radiator on my 91 civic, the heater operation symptoms you described were happening with me. Got warm at highway speeds but when idling the air would get cold. Classic water flow or low water problem.

No there is no fluids leaking anywhere, my overflow tank is full, I couldn't tell much about the radiator it was to dark outside, and sorry about the date thing this is my first time on one of these forums

If you are not leaking fluid then it sounds like water flow is not enough. If I understand how a water pump works, if it were starting to go bad, it makes sense that at higher RPM's then you would have more flow, but at lower engine speeds the flow is reduced to the point that the engine starts to get hot and the expanding fluids are vented through to the overflow reservoir.

And sorry for bringing up the cross posting issues, I guess I am still on autopilot from my years moderating IsoHunt, but I am not a mod here, so it is not my place to usurp their responsibilities.

If you learn more about what is happening, post and we will continue to help as best we can.