If you do not have serious pressure build up in the coolant system and just oil it is most likely a crack in the head or blown gasket between the water jacket and the engine oil. Usually this will result in more water or coolant in the oil than oil in the coolant, just depends on where the actual problem is located in the engine. With the bad miss associated with this problem I would start with a compression check on all cylinders, I would say that you are looking at a head gasket problem at best and a crack in the engine block at worst.



