I have a 2004 Honda Civic EX. My problems first started when my car would blow cold air when I went below 20mph and after that it would blow warm. Did that for about 6 weeks and I had it looked at and he said that I just needed to add a little antifreeze directly into the radiator that Hondas are soe times picky. Worked for about 3 weeks and then started overheating. I had the thermostat replaced and worked fine for about a month and then the cold air problem started happening again and then about a week later it has started over heating again. If I put antifreeze directly into the radiator it works fine for a day or two and then starts to over heat again. The reserve doesn't seem to go down at all. I could be wrong but I believe the mechanic said there wasn't a bleed valve on my car to release any bubbles....any ideas? Is my radiator bad or a blown head gasket or something else???

Thanks....

 

There isn't a bleed valve. To get the air out park the car level or slightly uphill so the radiator is the highest part. Turn the heater dial to full hot. Start with the engine cold and fill the radiator. Start the engine with the cap off and add more as necessary as it runs.

Running with the cap off and the radiator full, if you see a steady stream of bubbles when you rev the engine there is likely a problem with the head gasket. In severe cases coolant and air will gush out of the radiator like a geyser, so be careful.

The other thing it could be is a problem with the reservoir system combined with a leak to outside. If the radiator cap top seal is bad or there's an air leak in the hose to the reservoir, the radiator can become empty without drawing any coolant out of the reservoir.

 

Thanks for the reply. I tried your suggestion and I am not sure I figured anything out. When I pour the antifreeze in it bubbles a little when i goes down. When I reve the engine it will bubble a little when it goes down and then stops because it is gone. It seems like I could keep pouring it in and as I reved it, it would use the antifreeze. The cap seems really tight. It clicks twice and takes a little bit of strength to get it open.

Thanks...

 

Keep adding until it stays full. If it's really going away that fast, it'd be running out on the ground, inside the car (from the heater core) or blowing out the tailpipe (in big clouds of white "smoke" that smells like antifreeze.)

 

Wow, your engine was EXTREMELY low on coolant. I hope you have not permanently damaged the engine by overheating it.

 

Hey I have an 04 ex, I had the same problem and it was the head gasket, I waited too long and it overheated and warped the head.

 

how can the head gasket cause the car to overheat???
I am having the exact same problems with the same symptoms as described above.

 

Head gasket. 05 EX, my heat is intermittent, unable to fully burp the cooling system b/c air is getting in from the bad head gasket. I was quoted $800.

I would surmise lots of air in the system cannot effectively conduct heat, and there's your overheating problem. I didn't know these later 04/05 Civic's were prone to bad HGs...

 

Head gasket leaks let air from the cylinders force its way into the cooling system, where it displaces the coolant. With a bubble of air in the top of the engine the coolant can't flow properly, leading to overheating and heater not working.

To test, start the engine cold with the radiator cap off and rev it up. Air from a leak may bubble out. If it's a bad leak, air and coolant will literally blast out.

 

i have the same problem. what have you done to fix the problem?