coolant leak at overflow bottle
I had a similar problem. On pre-flight, found coolant on hangar floor below cowling, under passenger floor mats, and coolant spots all around firewall. Coolant overflow bottle almost empty. Bottle OK, cap breather hole OK. Diagnosis: leakage during previous day's flight at slip-on hose connection to bottle. Hose elasticity probably compromised, especially at bottle connection tube 'bulb'. I cut off 3/4" at hose end, reattached, but added hose clamp. Hose rubber at end of useful life? TT @ 230hours, Engine installed June, 2010.