I have read a dozen posts on this subject and still don't know where to go from here.(It would help if people would specify what solved their problem)
I have a '97 ex. My fan is working, I have a new radiator cap, the thermostat is less than a year old, my gauge never reads hot or moves after initial warm up, no CEL, and I tried leaving the rad cap off until water came out as one person said that is a way to bleed the system.

It seems to only boil when I have pushed the engine to around 5500-6000 RPM while driving, but I haven't fully tested that theory. So that might mean it's the head gasket from what I've read. But I have no water in my oil or steam coming out the tailpipe. My dad was a mechanic(never worked on Hondas though) and he doesn't think it could be the head gasket without water in the oil. So if someone is fairly sure that's it, could you explain why there's no water in the oil? Or does anyone have any other ideas? Oh yeah, I saw one post that said it could be the water pump. I don't think that's it, and even my dad said it should overheat if the water pump is bad.

 

mine would overheat at idle or stop signs, redlights, etc... if i was in motion or at a stop sign and put the rpms above idle the car would cool off. i could watch the temp needle drop down as i pushed on the gas. i was really confused and commenced to replacing the rad and thermo. no change. the problem didn't go away until i did the timing belt water pump kit. no i can run as fast or hard as i want and the temp does not go up.

mine was actually pushing the coolant out of the overflow bottle and running warm to hot. all this was cured with the water pump.

 

From personal experience, my Civic had a bad head gasket with no water in the oil. A small leak will just fill the cooling system with gases and push coolant out of the radiator like you describe. You may see bubbling if you run the engine with the radiator cap off and rev it up.

There's no water in the oil because the seal to the oil passage has not been compromised. A leak from a cylinder to the water jacket will not affect the oil.

 

Hello,
The overheating problem is never good for a engine and can cause many other problems that cause engine failure. The cooling system checklist is, fans are working,the themostat is working, the water pump is working, the the rad. is cooling, no leaks in the system. The worst is a bad head gasket or cracked head. One way to check for a bad head gasket is to pull the plugs and see if any of them look real clean due to water getting in and steam cleaning them. Hope you solve your problem, keep us posted on the the progress we all want to know how the problem was solved so we can help other members on this site. Thanks, 2010civiclx

 

Thanks for the help. I am thinking it is the head gasket now as I did run it with the radiator cap off this morning and I continuously saw air bubbles coming out of the radiator like mk378 mentioned. Not sure when I'll be able to get this taken care of(luckily I have another car to drive), but I will post the fix when I get it done.

 

Water boiling out the overflow tank is from my experience is cracked head or head gasket. I had this happen on a Lumina 3.1L V-6 we had & I drove it for 500+ miles with it boiling out the overflow. Yet no water in oil or out the exhaust. It was a cracked head.

 

Hopefully it's not a cracked head! I know some people are against this stuff, but I had some bars liquid copper block seal that I decided to throw in the radiator. While idling, the air bubbles have stopped coming out the open radiator cap. I'll post later if it actually solved the boiling problem......... well, at least for now.

 

The problem with most sealers is the plug the heater cores. & radiators. There is only a couple of sealers that won't plug & one is K-Seal it comes from Europe. The other is expensive & comes from Napa price is around $70. K-Seal is around $18. I have talked with several Mechanics in recent years that have warned me about stop leak sealers & these new Aluminum radiators & heater cores blocks & heads. The problem is the seal everything they block water passages also. One shop showed me an engine that the owner dumped Alum-seal in. It stopped the leak & shortly the cooling system.
So good luck. I hope you don't end up with a real major repair now.

 

I've heard all that before. Many times. I actually used this stuff when I first got the car because there was a small trickle of water leaking from somewhere that I could not find. It worked on that. I've also used it in several other cars I've had over the last 20 years. Maybe I'm just lucky, but I have never had a problem with any of those things you mentioned. My dad swears by the stuff as well and says it never did anything harmful to his cars. Anyways, the car is 13 years old and I have two other vehicles, so I'm willing to take my chances......

 

It yours Head Gasket....!! I know.. cuz happened to me and saw it the gasket problem after taken off the head.