PredatorCoder

Recently I replaced my heater box/core in my 1997 Civic with that of a 1999/2000 Civic as part of a climate control upgrade. (The previous heater box/core did not have any problems, e.g. leaking, and the new one doesn't seem to leak either). Everything worked fine, however I started to notice a few days later that the stupid radiator cap was leaking coolant. Both hoses going to the heater box were replaced - I don't observe any leaks around there. The exact procedure I did was:

1. Loosen radiator cap. Drain coolant.
2. Replace both hoses to the heater core along with the core itself. However one of them (the short one) was kinked cuz I was using generic hose from AutoZone, so I closed the valve allowing coolant to flow into the core just to be safe.
3. Fill coolant reservoir to MAX line. Fill radiator to cap.
4. Loosely attach the cap. Run engine for about 10 minutes.
5. Add more coolant. Tightly attach the cap all the way.

At this point I ordered the custom-molded hose from Honda so I could get rid of the kink. A week later, I found myself repeating the same steps above in order to replace the kinked hose with the Honda hose so I could reclaim the use of my heater core. But, I forgot to refill the reservoir in step 3... After running the engine and topping it off, I realized my error and did all the steps again (with the exception of replacing hose, obviously).

Seems like the only stuff I might possibly have done wrong was (1) use a kinked hose on the heater core for a few days, which wasn't allowed to be used anyway because the valve was closed - how would this matter?, (2) forget to refill the reservoir.... but this was corrected shortly afterwards.

The only thing I have observed is coolant leaking out around the radiator cap. The temperature gauge never goes to anything besides the normal temperatures it would reach before the work I did. So the cooling system (at this point anyway) still appears to be doing its job - the engine is not even close to overheating.

So do I need to replace the radiator cap? Or can I just replace the seal on it (is this practical)? Or did I do something worse to the cooling system and the leak around the cap is just a symptom? Did I not follow the correct coolant draining/refill procedure?

moores55

just replace the cap. come on man there like 5 bucks at autozone and it even says to change them when you change any of that **** out.

PredatorCoder

OK this is really getting annoying. I drained/refilled the radiator and replaced the cap with one from AutoZone as so many suggested I do, and it didn't fix anything. In fact, in the past the coolant temperature would not rise above normal. Today as I was driving to work on the interstate it actually overheated somewhat - temp gauge reached 3/4 (not yet in the red zone). When I stopped there was a lot of steam coming out from the hood. Opening it up, a lot of areas around the cap were wet with coolant. Steam was from coolant coming in contact with hot radiator/other stuff under the hood. Yet, the overflow tank was still at MAX which was where i left it when changing the caps. So obviously the cooling system didn't grab anything from overflow, yet leaked a bunch - thus the overheating. Something's seriously whack here.

Again, the cooling system worked *perfectly* before I swapped heater cores. The *only* changes I made were:
(1) Replace core with a (presumably) good one. It seems to work and have good flow - at least, when I turn temperature dial to heat, it blasts a lot of hot air thru vents, as expected. And there are no leaks.
(2) Replace the two hoses going into the core. One is an official Honda one. The outlet hose however is one I got from AutoZone. The diameter is a little less than the old Honda one - could this be the problem? Seems hard to believe, especially since the cap will leak even if I cut flow to the heater core by turning the temp dial to cool.

snatch

Seems like the problem may not necessarily lie within the heater core. Can you run the car with the hood popped and see any coolant leaking anywhere?

Did you possibly crack the neck on the radiator thus allowing coolant to leak out when the system is trying to pressurize?

Honda radiators are plastic, I can't imagine it would take a bodybuilder to crack them.

PredatorCoder

Would the smaller diameter in the core outlet hose for the heater core be the cause?

I don't know how I would have possibly broken anything on the radiator itself. I haven't noticed anything broken, and I never forced the cap on/off beyond anything normal.

When refilling the coolant I've run the car with the hood popped during the bleeding process. Also I've popped the hood immediately after going on a drive. I haven't observed any leaks around the replaced heater core hoses. The only noticable leak was the radiator cap (and of course a strong smell of antifreeze everywhere). Of course I did not really look much elsewhere, since everything worked fine before and I didn't touch most of the cooling system - thus I don't suspect a leak there.

Any chance this is causing a lot of damage to other parts of the vehicle or severely shortening their life span?

PredatorCoder

When I replaced the cap I also drained/refilled/bled the cooling system. The tank was filled to max at that time.

Just went out to the car again and looked at it, after it cooled down. Apparently the overflow tank accepted some coolant, because the coolant was definately above the MAX line. Then I removed the cap, and found no coolant at all under there (thus the overheating) - all I saw was bare metal fins in the radiator.

Checked the heater core hoses that I had previously replaced - verified that there were no leaks there.

No apparent damage to the radiator - the cap was on pretty tight, or so it seemed. Definately seemed to come on and off perfectly normally. So I think the neck is fine and not cracked.