Exhaust gas recirculation (EGR) coolers are primarily found in diesel engines. Their purpose is to process exhaust gases and lower emissions. They connect the intake manifold to the exhaust manifold and in most vehicles, they are bolted to the side of the engine, usually on the left cylinder head. EGR coolers vary in size and design, depending upon the size of the engine and certain emissions standards.
There are two chambers in the EGR cooler – an outer chamber and an inner chamber. Anti-freeze runs through the outer chamber and the exhaust gases flow through the inner chamber. As they run through the cooler, the anti-freeze cools down the exhaust gases as both are cycled back into the engine. The exhaust gas recirculation cooler can reduce exhaust temperatures up to 1,000 degrees by the time they reach the EGR valve. The most common gas an EGR cooler deals with is Nitrous Oxide (NOx) which forms at high engine temperatures.
When an exhaust gas recirculation cooler fails, the anti-freeze mixes with the exhaust gases and it produces heavy, white smoke that is discharged from the tail pipe. Other signs of a malfunctioning EGR cooler are a check engine light and a failed emissions test.