MBGT, what you can do is open up the radiator cap (cold) and put a radiator pressure tester in place of the radiator cap and crank the engine over, if it starts you can shut it off right away. Look at the pressure gauge and see if you get any readings. This will at least rule out head gasket leak from the cylinders.
What color is your coolant? Is it milky white? If not it could be that it's not oil as hot oil and hot coolant will blend and turn white. One test you can do here is add a dye (you can get this at most parts store) for oil and add it to your crankcase, run the engine for about 15 minutes and use a black light to see if you can see the dye in the radiator (make sure it is cool down enough to safely remove the cap, remove the cap slowly). Squeeze the upper radiator hose to make sure it's not hard as this would indicate high pressure (hot coolant).