Cusser
+1y
OK, I been thinkin' a little with my little brain: what would I do in this situation?
First thing I would do would be to take the oil drain plug off. Then I'd fill the radiator with plain old water, and see if any water comes out the oil drain hole. Take out the spark plugs and turn the engine over a bit with a wrench too while full of water, or maybe even pull the coil wire and crank a few seconds.
If there's really cross over between coolant and the oil systems, let us know.