There's a core plug at the back of the block. Though not likely, there is a big allen plug under the EGR cover that could be leaking, but would have to have a blown out egr cooler gasket as well to leak externally. Pressure test the cooling system if you are tring to find a cooling system leak (though I don't completely understand why you are so concerned about coolant leaking when your engine just caught fire from an oil leak).