This photo shows the other type of EGR failure that Bulletproof Diesel encounters regularly. Exhaust gases deposit gunk on the cooling fins inside the EGR cooler. This causes restriction within the unit. This restriction cuts down on the EGR's effectiveness, allowing higher exhaust gas temperatures to reach the intake manifold. Generally, this type of failure can be traced back to a clogged engine oil cooler. As the coolant side of the oil cooler becomes restricted, less heat is scavenged from the engine oil. This results in higher coolant temperatures and a lower volume of coolant exiting the oil cooler. As the restricted and hot coolant reaches the EGR cooler, the hot exhaust gases "flash-boil" the coolant in the adjacent channels of the EGR cooler. This failure usually results in loss of coolant from the coolant reservoir. This condition typically leads to a rupture failure of inside the EGR cooler, and eventually results in blown head gaskets.