I hate to be the bearer of bad news, but if the oil you drained was milky, the oil you replaced will also become milky. You've got more issues than a thermostat which is not working properly.
Cracked, head, blown head gasket, freeze damaged block... something is allowing water to enter your crankcase. For sure, condensation will not cause the oil to get milky like that. Even without a thermostat, and even if you were running in 33° F water, the head, coolant, and oil temperature would be well above the dew point after warming up, and any small amount of condensation which may have appeared would be boiled off.