Cadillac Deville 1994 Engine Coolant Problem

Start with the thermostat first

Allow me to elaborate with a few more details. When my car is not turned on, there is no leak. i can leave it sitting for a day or two and nothing will of spilled from the coolant container. It also doesn't begin to spill as i'm driving or just when I turn it on, it usually begins once i put the vehicle in park and turn it off. You're right the radiator isn't completely full as I only filled it a few days ago, but from what myself, my uncles and grandpa saw, there is no radiator problem. This happened twice, but in between a few days. The days it seemed okay after the initial spill, were significantly colder. Hope that helps, I at this moment in time believe it is the thermostat, and i will checking that when I get the chance (Sunday).