Water pump leaked a cup and then stopped?

[Earendil]

I'm out at my second track day of the year today. I've had no fluid leaks evident. After my first session I park it and walk away. 60 minutes later I return and find a puddle under my car. There are drops coming from the front of the engine. I do not have AC, and the water was a little orange (I use water wetter). I was missing approximately 2 cups of water.

I check the hoses. They are fine.
I look at the block, and it seems okay. No oil in the water, no water in the oil. I suspect the water pump gasket, even though it and the pump are only 6 months old. I start the car to see if the flow increases in order to pinpoint the source. The car stops leaking :weak:

So I go back out on track and keep a close eye on my low coolant light, but finish the session without a hitch. Park the car for another 60 minutes. Not a single drop was found or seen. I go out for a third session, and again, not a single drop
I checked my water level after each session and it was spot on.

So what happened? I'm doing another track day this Monday, and want to have the car squared away.

[Earendil]

Update:
Drove an hour home. Parked it in garage. Came back an hour later. Bone dry.
I was not imagining the leak. If it hadn't had water wetter in it I might have thought I sloshed water from some hidden compartment into the engine bay, but a secret stash of water that includes water wetter?

[jlevie]

If a pressure test of the cooling system doesn't find a leak elsewhere, a failing water pump shaft seal is a possibility.

A good addition to a track car is a coolant pressure switch and warning light. A pressure switch that trips at 3-4psi can tell you that cooling system integrity has been lost a good while before the temperature gauge reacts to the loss of coolant. I tee it into the small hose that goes from the expansion tank to the top of the radiator.