05: The factory oil cooler is a stacked plate heat-exchanger design. Coolant and oil flow through separate passageways stacked on top of each other. The problems with it are multi-faceted. First, the coolant in this high-compression motor, like most, has contaminants from multiple sources, ranging from supplemental coolant additives and gasket material to leftover sand from the casting process. These contaminants clog up the passageways in the cooler and reduce its efficiency, thus creating hot, less-dense oil for everything down the line to use for lubrication. The turbo, injectors, and HPOP (high-pressure oil pump) all take a beating due to this, and failure eventually follows.