Blow-By Filters

Its proper functioning protects the compressor wheel

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  • To prevent damage to the compressor wheel, filters and settlers have been installed in the recycling circuit
  • Inaccurate maintenance of a very simple system such as the blow-by filter can cause significant damage and substantial economic loss;
  • One of the most sensitive engines is the BMW 2-liter Turbo Diesel engine, for which the maintenance of the blow-by filter rather than being recommended is to be considered mandatory!


The engine is a system of moving mechanical parts and pressure is generated internally due to its dynamism. The only way to reduce such pressure is to create a vent to the outside. Unfortunately however, the exhaust fumes of the engine are carcinogens because they contain combustion residues and oil molecules. A new engine will have low pressure in the sump because the seal between pistons and cylinders will be excellent being ensured by new and not worn out piston rings. With time and use, the seal of the cylinders will be reduced thus letting in more pressure inside the engine and creating a greater quantity of gas. In order to reduce pollution, these fumes are put in circulation towards the intake of the engine or between the air filter and the compressor so as to burn all the polluting molecules.

To prevent damage to the compressor wheel, filters and settlers have been installed in the recycling circuit in order to keep oil droplets from directly hit the compressor blades. If the filter, called “blow-by filter”, is not serviced, the hose is partially clogged with the negative effect of increasing the pressure in the engine sump. This in turn will trigger a negative process where the pressure generated invades the chamber in which the thrust bearings rotate. At this point, there will be an oil leakage from the inside to the outside of the turbo passing through the rings both on the compressor and on the turbine housing. The oil that leaks from the compressor is combustible and therefore the normal stoichiometric ratio is altered with a consequent rise in temperature in the combustion chamber and greater particulate emissions (black powder). Under these circumstances the turbo starts to work bad because the particulate will collect on the turbine wheel, altering its balance and on the surfaces of the variable geometry, making the movement less smooth. Modern engines are equipped with catalysts or Diesel Particulate Filters (DPF): very often this is the cause of a clog in the exhaust system due to the excess of dust resulting from unburned particles with consequent breaking of the turbo because of the uncontrolled rise in gas temperatures and the increase of the axial thrust of the turbine rotor.

We can assert that an inaccurate maintenance of a very simple system such as the blow-by filter, can cause expensive and significant damages to engines. One of the most sensitive engine is the BMW 2-liter turbo Diesel engine, whose maintenance of the blow by filter is to be considered mandatory!

Blow by filters for BMW engines are available! Contact our sales office for more information and orders.

crossreference: turbocharger P/N, OEM references, applications


BMW 11127791552 700447-7 USBMW001
BMW 11127799224 708366-1  717478-1  731877-18  740911-1  741785-1  750431-9  750952-4  762965-17  49135-05670  49135-05720 USBMW002
BMW 11127799225 750080-1 USBMW003
BMW 11127794597 758351-2  758352-2  758353-4  765985-10 USBMW004
BMW 11127794175 5439-988-0045  USBMW005
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