It might be hard to see without taking the engine cowling off. If there a small leak you should be able to see a stain of dried antifreeze. I can say dont use any stop leak product. It will do either nothing or cause some other problem and ruin a seal, water pump, etc,

 

Hey, I thought I would put my 50 cents in (alluding to your coolant puddle size...make myself laugh...anyway). You are likely just looking at overflow. If you read the manual it will tell you that any loss in coolant in a sealed system is a potential larger problem. You could bring it in to be pressure tested.

The reason I know all this is that I am trying to get to a coolant leak of my own, that has been a pain (to say the least). I just posted on another thread and don't mean to duplicate, but if any one has ideas, I want to hear them!!

my car has 106,000 miles and the coolant reservoir empties out, usually overnight, when I park the car after I have driven it for a good bit.

I have a car guy that I trust and he is replacing my timing belt next week, but he and I have not found the coolant leak. I am hoping that when he "opens it up" that he will find something. Otherwise we are stumped. I suggested to him that it might be the Aux. Water Pump, but he did not think that was it. Should I tell him to replace the Water Pump and the Aux. Water Pump when he does the timing belt?? I would appreciate any thoughts!