Turbocharger and gaskets

Turbochargers and associated gaskets are crucial to the power output, torque delivery and fuel consumption of diesel engines in MAN and Mercedes trucks, buses and vans. The exhaust gas turbocharger uses the energy of the exhaust gases to pressurise the intake air via a turbine wheel and compressor wheel. This increases the cylinder charge: more oxygen mass enters the cylinders per power stroke than with naturally aspirated induction. Correct boost pressure and an airtight intake system are essential for complete combustion, stable exhaust gas temperatures and the proper operation of EGR and emission systems.

MAN D08, D20, D26 and D38 engines, as well as Mercedes OM 904, OM 906, OM 926, OM 934, OM 936, OM 470, OM 471 and OM 473 engines, use a range of turbocharger configurations. Depending on the engine variant and emission standard, these include fixed-geometry turbochargers, variable turbine geometry turbochargers (VTG), wastegate versions or multi-stage turbocharger systems. Control may be pneumatic, via an electric actuator motor or through an electronic control valve. Turbines, compressor housings, actuators and connection flanges are not interchangeable, even when the engine family or vehicle series is the same.

When replacing a turbocharger, the gaskets must also be selected correctly: exhaust manifold gaskets, engine oil turbocharger feed and return line seals, V-band clamps, O-rings, sealing rings and charge air pipe seals. Materials range from multi-layer steel gaskets and heat-resistant graphite to aluminium or copper sealing rings. They must withstand high exhaust gas temperatures, pressure pulses and the fitment of the specific flange connection. Parts must always be identified using the vehicle chassis number; visual comparison or selection based solely on the model name is never sufficient.

Loss of power, sluggish acceleration, black smoke, charge air pressure fault codes and increased fuel consumption often indicate insufficient cylinder charge. The cause is not always the turbocharger itself. Cracked charge air hoses, leaking intercoolers, porous O-rings or a distorted gasket between the exhaust manifold and turbine housing can cause pressure loss before or after the compressor. A leak on the exhaust side can also reduce turbine drive, meaning that the required boost pressure is reached too late or not at all.

Blue smoke, increasing engine oil consumption, engine oil in the pressure pipes or a whining sound may indicate worn plain bearings, damaged shaft seals or a seized turbine shaft. Play must be assessed with the air intake removed: limited radial movement may be normal on a shaft supported by an oil film, but once there is contact damage between the compressor wheel and compressor housing, the turbocharger no longer meets the required specifications and must be replaced with a new one. Axial play is generally more critical and requires comparison with the factory specification. Damaged blades often indicate a faulty air filter, ingested foreign objects or loose parts from the intake system.

First, read out fault codes and live data: compare the requested boost pressure with the actual boost pressure, check the position of the VTG actuator and assess the operation of vacuum lines, pressure converters or electric actuator motors. Then carry out a pressure test on the complete charge air system. Pressurise the system in a controlled manner according to the vehicle specification and locate leaks using a pressure gauge, smoke test or leak detection spray. Also inspect the exhaust manifold, flange faces and fastening bolts for soot marks; these reveal leaking exhaust gas connections.

In the event of turbocharger damage, always resolve the underlying cause rather than replacing the turbocharger alone. Clean or replace the oil feed line if contamination, coking or restriction is present, check for unrestricted drainage to the oil sump, and replace the engine oil and oil filter as specified. Fill the turbocharger with clean engine oil before the first start, start without applying load immediately and subsequently check for oil, exhaust gas and charge air leaks. Braem can provide technical support with chassis-number-based identification and the assessment of turbochargers and sealing kits.