If it was running hot, it could be something as stupid as no fan shroud, a bad fan clutch, or thermostat or radiator. If the lower hose was replaced, and one with no spring was installed, then the water pump could be collapsing the lower hose off idle. I'm sure it didnt drop 3 gallons of coolant out the overflow hose. So I would look over any and all of those ideas first. If it didnt mix oil and water, and wasnt smoking like it was burning coolant, I doubt you'll find cracks.