This is an example of a failed EGR cooler that caused a catastrophic engine failure. Notice the cracked coolant passageway (arrow). This unit failed because of a clogged oil cooler and excessive exhaust gas temperatures. This type of failure is typically caused by running an aggressive tuner or chip on a 6.0L with coolant flow issues. You see, the EGR cooler is the next place engine coolant goes after leaving the factory engine oil cooler. When the coolant side of the oil cooler is restricted, the EGR cooler cannot cool hot exhaust gases effectively. The EGR cooler was never designed to handle extreme heat and therefore develops a rupture or crack. When this type of failure occurs, coolant will mix with exhaust gases inside the EGR cooler-not good.