EGR VALVES
To reduce NOX emissions, some exhaust gases are recirculated through the inlet system and back into the engine cylinders again. This cuts the combustion temperatures at which these pollutants form. To reduce them further, the incoming hot exhaust gases can be cooled. This task is performed with an air-to-liquid heat exchanger that utilises the thermal management system to remove heat energy from the exhaust gas as they approach the EGR valve. You will find EGR coolers fitted to some Euro 4 cars but they are more common in later vehicles.
▶ Like other heat exchangers within the thermal management system, the EGR valve possesses hollow passages and thin aluminium walls so heat energy can transfer quickly to the coolant. The cooler is stressed not just by the continuous heating and cooling cycles but also the varying pressure of incoming gases from turbocharger engines in particular, which increase in the event of blockages, as pictured.
Failing EGR coolers tend to leak, causing coolant to enter the engine. Apart from a falling coolant level, look for excessive white steam from the exhaust and even increased engine ‘knock’. You may also notice performance reductions and even a lit MIL on the fascia. These symptoms, which also include bubbling coolant, may lead you to suspect expensive head gasket problems, when the EGR cooler is responsible. As the EGR cooler tends to be sited at the highest point within the thermal management system, they are vulnerable to air bubbles forming, which promote failure.
Before bolting on a new cooler, inspect it carefully for physical damage and give it a shake; there should be no rattles. As with all new components, compare it against the old part, so you are sure that it is the correct replacement. Check that the rest of the thermal management system is leak-free; if possible, conduct a pressure test. Once replaced, bleed the circuit thoroughly and check the engine management ECU for any lingering fault codes.