Kadams587

My civic has a very minor head gasket leak. The radiator started leaking so I replaced it. While bleeding the coolant system there were very small bubbles coming through after the system was bled (from the head gasket).
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If the car is blowing bubbles into the reservoir, does that mean that the excess pressure from the head gasket leak is being relieved since it's not part of the pressurized system? Or am I still getting excess pressure?

It's kind of hard for me to tell if the radiator seeping was from the extra head gasket pressure or just because it had 300k miles on the rad.
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TomCat39

Do a block tester test to confirm it's exhaust gasses.
The radiator tends to generate tiny bubbles at the neck and makes it look like you have air all the time as it cycles through it's processes.

These radiators have a plastic tank top that are well known to crack over time. I would suspect your 300K was the culprit.

The rad cap is 16PSI valve so excess pressure will always be relieved into the reservoir. I highly doubt pressure can build enough to crack the plastic tank normally.

Kadams587

I did use a block tester when I first suspected the head gasket issue after the car overheated. The testing fluid barely changed. Went from blue/purple to basically the same color with a tiny hint of green. Didn't go full yellow or even close. The car doesn't seem to be burning any coolant and the oil looks normal.

I'm fairly certain the bubbles are exhaust gases. Revving the engine slightly produces a steady stream of tiny bubbles, and at idle it will let a small/medium sized bubble out every 10 seconds or so. Seems like without the extra flow from the rpms the small bubbles build up and are eventually forced out when it builds up slightly.

I only plan on driving the car a little while longer, I'm just worried it will leave me stranded if excess pressure decides to pop a hose or something.

mk378

Leaks of any sort seldom get better over time.

The exhaust gases displace coolant out of the engine and radiator, leading to overheating. That is the main issue with a small leak.

Kadams587

Haha yeah, I wouldn't assume it would get better with time. Basically my question was whether it was safe to assume that because the system is relieving those gases into the reservoir, that excess pressure wasn't building in the system. The coolant level in the system stays full, the reservoir level doesn't move, and the car doesn't overheat.

I'm just hoping to get another month or so out of the car, already looking for something new.