03 Civic Heater blowing cold air at idle

[eggbrook]

Like the title says, my 2003 Honda Civic EX is blowing cold air at idle. This is a sudden problem, I figured since it had never had a coolant flush I might as well do one and get clean Honda OEM coolant to replace it. Well it worked for a while, I bled the system nicely following the repair manual from Honda and it was great, heat was back at idle everyone is happy. Until suddenly over the last week the air has started getting cooler and cooler at idle until now where it is just blowing cold air again at idle only. I am at a loss here, why would it suddenly begin blowing cold air again. I am wondering if it could be a bad radiator cap that is letting air into the system, I just bought a replacement cap online it'll be here on Tuesday, and hopefully that will fix it. Anyone have any ideas? Also the thermostat on this vehicle is pretty new I replaced it with the coolant flush, car has 90k miles on it so I figured why not it wasn't expensive.

 

[sr6000]

Are you losing coolent slowly but not finding any on the ground

 

[eggbrook]

I think so, I added more coolant and bled the system today and replaced the radiator cap. The coolant was low, but I haven't seen any sign of coolant leaking. I am starting to think its the head gasket and the engine is burning small amounts of coolant

 

[MarieC]

I noticed this happening to my car a few months ago. The heat only worked if I was actually working the car - freeway or uphill, idling and downhill it would just blow cold air. I took it in for normal service a few weeks ago and they forgot to check (or drained for some reason) my coolant. The car immediately started overheating, I took it back and they added coolant, sheepishly apologized and sent me on my way. 2 days ago my car started overheating again, I took it to another mechanic and they said that I have a blown head gasket. My new mechanic says that it's not the other mechanic's fault - it looks to him like I've had the problem for longer than 2 weeks and they actually did me a favor by bringing the problem to my attention. He also said that most of the people who come to him with blown head gaskets complain that their heaters don't work but he's not sure what the relation is.