I want to talk today about EGR cooler failure in a 6.7L and compare the system to the 6.4L. This is an EGR cooler in a 6.7 that is clogged on one side so there is no flow through. This particular engine behind me (6.4L), for comparison purposes, came from an ambulance with 120,000 hard miles on it and almost 2,500 hours of idle time.
The 6.7L has a cooler on the EGR system where the exhaust cools down in a cooler before it goes into the intake. Exhaust gas recirculation (EGR) means that exhaust gas goes back and gets reintroduced into the intake and run through the engine and burnt one more time. It is the same idea as a gasoline motor. It reduces the nasty stuff that comes out of the tailpipe. On the 6.7 the intake comes from the outside instead of the exhaust manifold on a 6.4. What happens is it passes through the EGR valve first so that the EGR valve is on the hot end which keeps the EGR valve on a 6.7 clean. But it goes through the one side of the EGR cooler and then out the other side so there is a cool side. The cool side of the EGR system regardless of whether the valve is on the beginning end or the back end is going to be the side that clogs.
The diesel engine doesn’t create heat like a gasoline engine. A diesel engine creates heat only when it is under loads. When it is idling, it is running very cold. If a diesel engine is not being pushed then it is not going to burn off these hydrocarbons especially with idle times like this where a truck will sit for 10, 12, 14 hours just idling. So you get this buildup inside. This is a common EGR clog.
You cannot stop coking in the EGR system due to idle. I don’t care what kind of design you have. It is impossible. Whether it is Chevrolet, Ford, Dodge, Cat, whatever, idle time will clog up the intake system. It is just a fact of life. However, the 6.7 is such an improvment over the 6.4, because the EGR valve is on the hot side of the 6.7 and all of the carbon gets burned off, it is very seldom a problem so that expensive component stays clean. On the 6.4 though, the EGR gases come in at the back of the lower EGR cooler and goes through the upper EGR cooler and the cold part is over by the valve. If the valves had been on the back side where it was hot, it wouldn’t have been a problem.
Another benefit of the design improvement in the 6.7L is the replacement and maintenance cost. There are two EGR coolers on a 6.4L; the lower is about $500, the upper is about $400. Usually you have to replace both of them with a tremendous amount of labor involved. On the 6.7 the part is cheaper and it is much easier to get to. The parts and labor cost is much lower than it is to disassemble half the engine in a 6.4.
How do you keep these things from clogging? Just go down the road and blow the carbon out of it. Just like the old days – drop the hammer and keep running it until the smoke quits coming out the tailpipe. It will clean itself. There is no cure for coking up the EGR cooler with idle time. If you are idling the vehicle all day and night, this is what is going to happen. ~Bill Hewitt