Over the winter and for the past few winters I go to my sisters house in New Hampshire for Christmas. The car sits outside overnight with the temps in the 20's. When I get up in the morning I always have a small 6" pool of antifreeze on the driveway beneath the radiator. I check the drain plug and it is not wet so I know it is not comming from there or the radiator hoses. Why do I not get this during the spring and summer. Only during the winter. I can't find any leak.