The warning buzzer/light goes on everytime I stop my car after a drive. It doesnt come on while I'm driving nor does it come on after the car has been sitting for awhile. I look under my car after letting it sit and sometimes I see a small puddle of water/coolant mix under the overflow resevoir. I check my coolant everytime before I start my car and its always full.

So, whats setting off my warning buzzer/light? Could the sensor be off/broken? I have a feeling my resevoir is cracked because when I try to fill it up to the min line it always leaks out. (I'm going to be replacing it. Anyone have one for sale?)

I hope the cause is something small and not a problem with my motor. Its a reman with ~40k on it.

Any help/suggestions would be greatly appreciated.
Thanks!