mysterious coolant leak
 

Our 2001 S80 T6 has developed an erratic leak. It does NOT do it every day, but sometimes in the morning when we move it out of the garage a spot of coolant about the size around of a golf ball is on the floor. I have got up under the car, checked under the hood, and found no leak visible anywhere. Also, even when cold, when you start the car, the temp gauge automatically bounces to the middle, instead of slowly going there while it warms up. This evening, after having parked in the garage for about an hour from a 8 mile drive, I went out, and the cooling fan had clicked on.......hmmmmm.

The car is NOT over heating, drives fine, no smoke or steam issues.....just has me a little curious...and perhaps a bit worried. Anyone know where to "start" trying to find the problem? I have thought it could possibly be a thermostat....but may be way off in my thinking. Any and all input will be greatly appreciated!!