TL150 Coolant Problem

My machine has the coolant level sensor, I have a bypass wired up that I typically use when digging or load/unload from trailer. My overflow bottle has been puking water out while running and after 3 or so hours the machine shuts down from low coolant. I allow it to cool and add water until its full and go at it again. Its typically worse early morning on initial start up until the engine warms to operating temp. My personal opinion is a head gasket leak causing air to pressure up in the cooling system... Or maybe a stuck thermostat??? Just wanting some opinions before I tear into it in the near future. Thanks