Headgasket question

[Benfolio]

I know they're bad. They HAVE to be bad.....

Anyways, my car pushes coolant into the overflow, yadda yadda, BUT. Only when I turn the heat on?

I bought a JDM motor, headgaskets, timing belt, the works because I KNOW it needs it. I'm in the process of getting it ready to swap into my car in the near future (rather than rebuild my 165k original motor). But I had to go on a trip last weekend, old crappy motor and all, and since I noticed it pushes out LESS coolant when the heat is off, I drove the whole 160 mile trip with no heat. FUN!
It pushed out just a tad of coolant, about normal. Just enough to raise the level in the bottle halfway from low to full. When the car cooled, the coolant level went down as it should.

BUT, like this morning, if I run the heater AT ALL, the level goes from low to above full, in just 15 miles of driving! And I bet if I go out there tonight to go home, the level will still be high.

Please someone explain this, it's driving me nuts!

Only thing I can think of is that the t-stat is barely opening (even on the highway at 75MPH for an hour) keeping all the combustion gases trapped when the heat is off, and SOMEHOW the t-stat is opening MORE with the heat on, letting the gases out into the radiator, pushing coolant into the overflow bottle.

Or?

[Huffer]

Well... normally I'd never say "HG failure" unless you're actually losing coolant from a leak, or you're seeing oil or bubbles in the coolant. What the coolant overflow bottle does is...whatever it does. :lol:

Try testing the t-stat. You know, sometimes people like us freak out when we see cars that do things "they're not supposed to" but they're actually normal.

[Benfolio]

Oh I get bubbles in the coolant (not so much oil) and it smells like crap. T-stat is new, but i had the same issue before and after I replaced it. Otherwise it comes up to temp properly and doesn't fluctuate.