The EGR cooler was added to the Ford Powerstroke to help with emmissions, suppossedly protecting the environment. EGR cooler failures cause (in my opinion) about 80% of the failures with the 6.0 Powerstroke engine. These failures create a huge amount of scrap metal, oil, anti-freeze, and air polution from manufacturing and transporting all of the new parts.
I believe our EPA screwed up when they created all of these problems, causing more environmental damage than if they would have left things alone.
The EGR cooler is designed to recirculate some of the exhaust gasses back through the intake in an effort to re-burn some of the unburnt diesel fuel. Before the exhaust gasses can go into the intake, they need to be cooled. The EGR cooler has a water jacket that can eventually corode from the caustic exhaust gas causing it to leak. If it leaks, coolant is sent directly into the intake and therefore, into the cylinders. Water (coolant) can not be compressed and causes the piston to push the water against the head much the same as if the piston itself just became taller. Banging on the heads cause head gasket failure because of the TTY (torque to yield) head bolts that Navistar used to assemble the engines. The TTY bolts stretch causing the head gasket failure.
Another more catastrophic failure can happen if the amount of water entering a cylinder is excessive. A connecting rod can break sending it through the block.
An entire industry was created to "fix" all of the problems created when the U.S. Environmental Service dictated that diesel engine emmissions needed to be reduced. The problems are not at all limited to the 6.0 Powerstroke or just Ford engines. Every brand of diesel engine has considerable problems and failures created by the "so called" environmental protection laws.
Of course the IRS has been the beneficiary by collecting all of the taxes from this newly created industry.