Hello, I've noticed my coolant level dipping a bit over a couple months so last night I filled it to about two thirds between Low and Full in the overflow reservoir. The car hadn't been run a whole day before that. Today when I checked again, the level had dropped to about half way between Low and Full. During all this time, the car was sitting in the garage and wasn't started at all. The temperature was down to about 10 degrees F last night and in the teens during the day today. Can this be attributed to the cold? No signs of leaks. The upper radiator hose had a leak that was taken care of last year. The water pump was replaced last spring. Any ideas?