Oil in radiator

My car started running rough and I turn it off and checked everything and found oil in my radiator. The oil stick said 2 qrts. low and i replaced it. What next ?

Make/model/year/miles?

Make, model, year, engine and transmission type?

First thing to do is determine whether it’s motor oil or automatic transmission fluid in the radiator.

1998 Honda Accord 199,000 miles on engine. It is a 4 cylinder. It looked black.