How EGR Works

An EGR cooler is exclusively on diesel engines due to the extremely high cylinder head temperatures associated with high compression. It sole purpose is to prevent nitrogen oxide emissions into the atmosphere.

Diesel engines rely entirely on high compression to ig

MTU Integration EGR in engine design

MTU Integration EGR in engine design (Photo credit: Tognum: MTU & MTU Onsite Energy)

nite the fuel as compressing diesel fuel creates heat sufficient for ignition. Just like automotive gas engines, this high cylinder head temperatures form nitrogen oxides or “NOS.” This is a primary cause for the “green house effect” in our atmosphere.

A diesel has higher cylinder head temperatures than a gas engine so introducing exhaust gas directly into the cylinders would only raise the temperature even further. For this reason the exhaust gases must be cooled before being introduced into the engine.

The EGR cooler has been a sore subject on diesel engines, especially the Ford 6.0 liter for some time. EGR cooler failure is a major cause for catastrophic engine failure.

Exhaust gas travels from the passenger side exhaust manifold through a metal pipe to the EGR valve under the intake manifold. When the engine rpm increases above idle, the computer opens the EGR allowing exhaust gas to flow from the EGR through a pipe that runs along the underside of the passenger-side intake manifold and into the manifold.

The EGR cooler is the long pipe from the EGR valve that is fitted with a radiator core on the inside of the pipe. Engine coolant passes through this small core and cools the exhaust gas passing over and around it.

Herein lies the problem, and the solution. The factory EGR cooler has very small and easily clogged cores. The engine coolant first passes through the engine oil cooler located at the rear top of the engine. From the oil cooler the coolant passes through the EGR cooler and then back into the radiator.

The EGR cooler plugs up with casting sand left from the engine casting along with particulates in the cooling system. When this happens the engine coolant flow is reduced and the engine begins to overheat. Now the exhaust gas accelerates the heating of the now immobile coolant in the cooler and causes the oil temperature to rise.

This causes the engine to blow a headgasket or possibly ingest enough non-compressible coolant in a cylinder to break a connecting rod.

The correction is to install an aftermarket bullet proof EGR cooler that uses aluminum tubes as opposed to radiator cores. It will not plug and is much more efficient at cooling the exhaust gas.

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