don't forget the intake stroke this would suck coolant in but ya it possible for coolant to flow only one way. Take off your cap and see if you get a lot of bubbles.

 

The radiator cap has "1.1" stamped into it. I assume that this is a 1.1 bar cap. It is a replacement cap but it is not OEM. The cap goes on and off easily, about as easy as the stock cap. I know the cap allows coolant to flow into the reservoir so at least that part of the cap is working. It's not flowing out of the reservoir and into the radiator. I'll check for bubbles.

 

Sounds like you might have the wrong pressure cap.

 

Disregard my last post. I misread that you had the 1.1 cap. That is the correct cap.

 

From what I've seen with headgaskets, anything is possible. Usually they fail in ways that make sense, but sometimes you get strange results or a headgasket that only leaks under certain conditions (common on boosted cars). However, if your car held 15 lbs of pressure without bubbling the coolant... headgasket problems seem unlikely. I wouldn't 100% rule it out, but I'd look elsewhere.


However, this seems like an annoying but harmless problem. You said a mechanic is doing things, you're not throwing a bunch of money at this are you?

 

Sorry I took so long to reply a post. The pressure check was on the cooling system. I still have not done a compression test. However, I finally checked the cooling system running the engine from a cold start with the radiator cap off. I can see a steady stream of fine bubbles percolating in the coolant. I have not put any money into troubleshooting this problem, except for replacing the radiator cap (which needed replacing anyway). I have a strong suspicion it's the head gasket, which means I will be out more than a few bucks. I keep adding about a pint of water everyday just to keep the radiator topped off. Other than that, the engine runs fine. I am just going to keep doing this until I know what the problem is for certain. I'll submit posts as new events occur. Thanks for the advice guys.

 

My cooling system was still overflowing out of the reservoir tank and I figured there was one thing that I could do before exploring the possibility of a leaky head gasket. I thought I would replace the thermostat, which would cost me about $10 and some time. Ever since I put in the new thermostat a couple of days ago, my cooling system seems to be stable now. No leaking, and no temperature fluctuations (the engine temp used to drop considerably especially during coasting). I thought the thermostat needed replacing when it stopped the flow of coolant, causing the engine to overheat. Apparently when the stock thermostat failed, it stayed stuck open allowing the engine to run below normal temperatures. I guess I should have paid more attention to my temperature gauge to know where the needle was during normal operation. Now the needle stays in the same place and doesn't hardly move at all.

As far as seeing the bubbles in the system, I figure that might have been residual air in the system. Other than that I can't explain it. Once I put the new thermostat in, I checked for bubbles again and there were none.

Anyway, everything seems fine so far. Thanks again for all the advice. Hopefully this will help someone else someday.

 

I had the same problem until I replaced my radiator cap

 

i had a similar problem too, but i'm unclear as to why an open thermostat would affect the fluid not wanting to go back into the radiator from the overflow tank.

 

What was causing your problem? I am also curious as to why a faulty thermostat would keep the cooling system pressurized , which is why the coolant would not flow back into the radiator. Every time I opened the radiator cap, it was like opening a pop bottle. I wonder if Honda has a service bulletin on this...