An oil cooler leak on a diesel can manifest itself in several ways, but critical in every case and requires immediate attention. Oil flow and temperature as well as EGR cooling are the two foremost problems with most diesels-especially Ford 6.0 liter engines.
The coolant and oil temperatures must always remain within 15-degrees on one another. This is critical to prevent oil breakdown and engine overheating. One of the biggest oversights in the design of the most popular diesel engine, the Ford 6.0 liter, was the size of the oil cooler and the EGR cooler cooling surfaces.
The EGR cooler is a long pipe on the passenger side above the valve cover designed to direct exhaust gases to the intake manifold. In order to cool these gases to the appropriate temperature a radiator core similar to a heater core is placed inside the pipe. Coolant passes through the radiator core inside the pipe to cool the gases passing through the pipe and around the core.
The radiator core is subjected to a constant 1000 to 1500-degree heat from the gases and an outside pressure of 50 psi . Due to the large amount of soot created by a diesel, the inside of the cooler pipe accumulates enough soot to impede the flow of exhaust gases. On the other hand, the core itself becomes plugged internally with scale from the coolant system, sand from the casting process and gel from the overheated coolant.
If you experience no driveability problems although it is necessary to top off the coolant level in the radiator often, it is likely that the EGR cooler hose is leaking.
If steam can be seen coming from the exhaust and you experience a power loss coupled with a poor idle, the EGR cooler is leaking internally and must be replaced. This is a serious situation that will eventually result in either a blown head gasket, engine coolant blowing out of the coolant reservoir, bent rod or broken piston and oil in the coolant.
When the EGR cooler leaks, the core allows coolant to enter the intake manifold. A large leak generally will cause back-pressure to enter the radiator and cooling system causing the engine to overheat as well as the engine oil.
A dealer will charge $2800 or more to replace the EGR cooler. Although it looks intimidating when first gazed upon, it is not very difficult to replace yourself and save thousands of dollars. It only takes two to three hours to complete.
Replacing the EGR cooler or hose requires the removal of the batteries, air intake ducts, turbo intake duct, turbo, intake manifold and finally the cooler. Get a service manual at your local auto parts store. It will give an in-depth procedure with illustrations to make it easy.
The EGR cooler and oil cooler are the only two major problems with a Ford diesel engine. Replacing the old cooler with an OEM is much like placing a Band-Aid on the problem. Purchase an after-market bullet proof cooler that uses aluminum tubing rather than a radiator core to cool the gases. It will not crack or fail like the original.
At the same time while the manifold is off, replace the oil cooler as well since it has the same deficient core inside. The new oil cooler comes with an adapter bracket and moves the oil cooler to a different location near the radiator. It uses the same type of tubing and will not clog either. Replacing these two coolers will result in a much more reliable engine and protect your investment.