A clean solution

The EGR coolers from MAHLE

In our “Introducing a product” series, we give you the essential information from the experts about different vehicle technologies and equipment in a compact, uncomplicated form. Here, the focus is on the exhaust gas recirculation cooler, or “EGR cooler” for short.

The function and principle of the EGR cooler


The principle of the exhaust gas recirculation cooler is simple: Some of the primary exhaust gas flow between the exhaust manifold and the turbocharger is guided to a special heat exchanger (EGR cooler), where it is cooled down and then fed back into the intake air. This cooling decreases the combustion temperature in the engine, decisively reducing nitrogen oxides.

The structure and operating principle of the EGR cooler

EGR coolers are made of either stainless steel or aluminum and installed close to the engine. Both hot exhaust gases and coolants can flow into the cooler via several connections. After the exhaust gases have been cooled down, they are discharged from the cooler in a controlled manner via the intake system back into the combustion chamber. This leads to a reduction in nitrogen oxide emissions—even before reaching the catalytic converter. The exhaust gases returned from the cooler to the combustion chamber are dosed and controlled by pneumatic and/or electric actuators on the EGR cooler.


Possible defects and failures in EGR coolers

You probably won’t need to replace an EGR cooler very frequently—it isn’t one of the “classic” wear parts. Nevertheless, it is possible for various defects and related failures to occur:

  • Extreme temperature fluctuations as well as missing or aggressive coolant additives can lead to internal or external leaks.
  • Above all, a gradual coolant loss indicates a leaky EGR cooler—frequently in connection with increased engine temperature.

Dangers and consequential damage from defects in the EGR cooler


Even if this may initially remain undetected due to the higher exhaust back pressure in comparison with the coolant pressure when the engine is running, mechanical damage to the engine components is possible as a result of coolant accumulation and “hydrolock” when the engine is restarted.

If there are cracks in the EGR cooler, the exhaust gas pressure can escape uncontrollably. Inadequate boost pressure coincides with a drop in engine performance. Other defects are leaks, torn membranes, and electrical or mechanical defects in the actuators used. In addition, the EGR cooler can carbonize.

Many of the specified defects cause the engine lights to illuminate via the control unit.
Please see the appended practical troubleshooting tips:


Customized cooling solutions from MAHLE

With the modern MAHLE EGR coolers, we make it possible to achieve the strict Euro 6 limits for the emission of nitrogen oxides (NOx). With the acquisition of Behr Hella Service in January 2020, we at MAHLE are once again strengthening our competence in the areas of cooling, air conditioning, and ventilation, while further expanding our vehicle part range. Thus, we are able to combine superior original equipment competence with a complete product portfolio. In addition, both trade as well as you in your workshop benefit from our global logistics network.


We regularly provide technical tips relating to the powertrain, thermal management, and mechatronics in automobiles.


MPULSE - The magazine

The print issue of MPULSE will come out twice a year.