Small coolant leak

[DLinkOZ]

I have what appears to be the seemingly common leak between the end tank and the radiator core. My wife got home, parked in the garage as normal. I went out a few hours later, and saw some liquid on the ground. It wasn't a huge amount, my first thought was "wow, the AC condensor is sweating like crazy today." Upon further inspection, it's coolant. She says there were no lights, everything was normal. In hindsight, last weekend at a family member's house I had the same "wow, that's a lot of moisture off the AC" thought and we've driven quite a bit since then. It's odd, so some details.

Background and additional information:

I had a thermostat stick closed on Christmas Eve, things got pretty hot for a very short time (minute max, just barely hit the top of the gauge). My guess is that pressure may have weakened the gasket on the tank. Strange thing is it didn't leak out that much last night, and none today after driving it to Wal-Mart. During that 5 mile trip, the thermostat opened, the engine stayed cool, and as of right now there's not a single new drop on the floor (I parked to the side a little so I could be certain). But the fact is last night it dumped probably 4 cups of coolant on the floor. When I filled it up, there was about 1/4 of the degas bottle empty. The leak was all above the inlet hose (but did not seem to be the hose itself), no further up than the lowest row of fins and seemed to puddle between the right plastic tank and the core in the cavity where the core clamps to the end tank.

I don't plan to take chances, and plan to replace it. But the fact that it's no longer leaking, even after full cycling of the entire system (thermostat opening, etc), makes me scratch my head a bit. Is there anything else that could cause this odd behavior?

 

[DLinkOZ]

Quick thought - could it be that it just takes a good amount of heat to cause the tank to separate a bit, causing the leak? Both weekends with leaks, versus in between with no leaks, shared a common difference - the two weekends with leaks involved quite a bit of driving (hour or more), where the days in between had smaller drives of only a mile or two each (taking the kids to school and picking them up, and a few trips to buy groceries). Anyone with more knowledge than myself think that idea holds water? Even if it does, still calls for a replacement radiator.