Hello, I have a '05 Civic EX Special Edition. It has been running hot for a long time but only actually boiled over a few times. There is too much pressure in the radiator. When it's warm the coolant goes into the overflow tank and when it's cold it doesn't go back into the radiator. Had the timing belt and water pump replaced about a year ago. I replaced the radiator cap, coolant temp sensor, cooling fan switch and thermostat (3 times). One time it boiled over it blew the cap off the overflow tank. So I replaced the overflow tank and cap. I flushed the cooling system too. And I did a combustion gas leak test that showed no sign of carbon dioxide in the cooling system. I do delivery work in it and put about 60 miles on it every day. The only way to keep it from running hot is to burp the air out of the cooling system...every day. Does anyone have an idea of what could be wrong with it?

 

Your headgasket is blown allowing exhaust gases to pressurize your cooling system. It is common on Honda products. It will only get worse until you overheat the car resulting in catastrophic damages. Get it fixed.

 

Thank you Ed! There is no white smoke and the oil is not milky. I did a combustion gas leak test on the cooling system and no exhaust gas. That's why I didn't think it was the head gasket.

 

It seems that the headgasket failures, at least the ones that I personally have experienced either on my own vehicle or on a co-workers many Honda Civics that he has for his 5 kids, are very subtle and somewhat intermittent, at least at first. Another thing noted on our cars is that the temp gauge will not always show a problem. We surmised that the gas bubble that has replaced the coolant in the system does not get hot enough to accelerate the gauge to the hot zone. Just a guess there.

The pushing of the fluid into the reservoir then out the reservoir drain tube will not allow it to be recovered during cooling/suction since it has been depleted a little bit on each occurrence. If you look closely around that drain tube you should see white deposits showing its exit. Headgaskets, while fussy, are not beyond the scope of a capable DIYer. Read, research, and label label label if you decide to do the job. It took me about 8 hours on a 1994 last time, but I am way careful, as in cleaning the head bolts on a wire wheel, setting the valves, etc. If you go to a mechanic, I would suggest you provide genuine Honda parts, including the coolant. I am, as I said, way careful.

Good for you for looking for tell-tale signs. The failure isn't catastrophic enough to leave clues (at least in the beginning). I even closely inspected my failed head gasket once the head was off and had a hard time finding the breach.

Good luck.

Ed

 

I also have an 05 EX special edition coupe. Before you get into tearing the whole thing apart for a head gasket problem, I'll suggest you get a new thermostat and get an original one from the dealer. I had the same problem. Replaced thermostats and overflow tanks a few times. Turned out to be the Stant thermostats I was using. When you get an original, compare it to a replacement and you'll see there's quite a difference between the two. Good luck.
Duane
P.S. Get an original equipment radiator cap, too, while you're at the dealer.