Rep Power: 0

BEFORE SERVICING YOUR COOLING SYSTEM MAKE SURE THE ENGINE IS COOLED OFF BEFORE REMOVING RADIATOR CAP OTHERWISE YOU CAN SERIOUSLY INJURE YOURSELF.

My 2001 civic ex kept pushing coolant out of my overflow tank and my idle was very low at around 550 rpm, NO Vaccum leaks at all. Also my headlights would dim while giving gas and brighten while letting go of the gas pedal. It seemed 100% reversed. Everyone right away said poor idle is head gasket specially if i had coolant overflowing thru overflow tank and lights going dim was alternator or battery 100% WRONG.
I did not have white smoke out of the tail pipe, spark plugs dry no sign of coolant, radiator held pressure at 16 psi for 10 minutes without any leak and car ran strong without hesitation or power loss. Rpm would drop at the light, stop sign or while parked but ran strong on the highway.

WHAT SOLVED MY PROBLEM
On the bottom of the radiator there is 3/8" hose if i remember the size correctly that runs underneath the fans from left to right. What happened in my case was end of the hose collapsed 1 inch above the fitting at about 85% closed. I have replaced that hose and NO MORE OVERFLOW. I flushed the system twice and put in new thermostat and radiator cap form HONDA around 40.00 for both before filling the radiator with new coolant. Make sure ALL AIR IS OUT of your cooling system and use 50/50 mix.
I tested my alternator and battery and everything came back good. I brought my car to advance auto (2nd opinion) and had them run the test and give me result print out. It confirmed that charging system was all good. Cleaned up my ground wires on the body of the car and it seemed to solve my dim headlight issue for now. I have done coolant flush battery, alternator test and ground wires cleaning same day.

If you are still reading this my idle is back to normal and my lights don't dim anymore. Check for collapse hoses and change your coolant fluid a lot of people over look this part of maintenance and its very easy to do just don't burn yourself. Make sure you get all the air out of your cooling system...

Good luck to all.

 
Rep Power: 210

i wouldn't consider it "fixed" or your problem "solved" unless you are symptom free for about a month,

i have a funny feeling you will be overflowing with coolant again in the near future,

your symptoms just reek of a failing head gasket

 
Rep Power: 519

I concur.

 
Rep Power: 0

Everyone told me I had a bad head gasket too when I started overflowing from the tank, I did a block test like 20 times and it never detected any gasses in my cooling system. I replaced my thermostat and radiator cap and so far it's seemed to fix it, I drive 80 miles a day 5 days a week and it hasn't reoccurred.

Could it be failing ???? Possibly... but my car runs awesome and gets 37 mpg all day long...

 
Rep Power: 211

A block test isn't the gold standard test for a headgasket breach as there are several types and symptoms of headgasket failures: http://www.holmanparts.com/wp-conten...dGasket_V2.pdf
Injecting air (100-150 psi) into the cylinders via the spark plug holes while pistons are at TDC and watch/listen for coolant bubbling in radiator is the best method of detection. The strongest symptom of a head gasket breach in Honda engines is coolant loss in radiator with coolant gain in reservoir. In your case the the radiator cap was most likely the culprit.

Hopefully, the OP's issue is truly solved. If I were him I'd want to ease my mind by injecting air into cylinders a-la ezone method to know for sure.

 
Rep Power: 229

...it sounds like you opened up an atf cooling line, not a coolant line. on the 01-05 civic ex there are two large hoses that lead to the engine, one small hose into the overflow and two ATF cooler lines (as well as ac lines on the ac fan side).

 
Rep Power: 148

I had the overflow problem recently. I took the overflow reservoir out, emptied it completely and refilled it at the minimum level. Drove around for an hour with AC on. Came back and checked. Coolant was at the correct level, no more overflow. It's been two weeks, so far so good. No over heating or overflowing and it's been in the 90's here for the past week.

 
Rep Power: 0

Since when did Honda use hoses on ATF lines that can collapse?

 
Rep Power: 0

After a few days I noticed the same issue occurring again. Turns out my system was over full. I had to monitor the flow between cold and hot for a few days but eventually I got it leveled out and now it stays leveled and doesn't over flow.

 
Rep Power: 148

The same thing happened to me after the last oil change. The guys who changed my oil overfilled the reservoir and radiator. I emptied the reservoir and drove around then filled it to the correct level and it has been fine. It isn't always a bad head gasket.