Attached is a simple diagram of a head and block of an engine. In a boxster it would be different as there would be two on either side, but the general concept is the same. In the head, or cylinder head, coolant and oil run in their own separate channels. Coolant cools the engine down, and oil lubricates. This is the main function of each. Oil usually will not cool an engine adequately, and coolant cannot lubricate the internal parts of an engine. When failure like this occurs and the milkshake mixture is present, it means that there is a crack in either the head or the cylinders of the engine that is allowing these two to mix. Because coolant is now in the system, and it cannot lubricate, all of the engine components deep inside the engine are now wearing out incredibly fast. If this is the case, then it is likely too late to save the engine in its present state. Sooner or later, even if you replace the head, the damage caused from driving the engine with that mixture will cause it to fail prematurely.
