Airfilter

The air filter element protects the engine against dust, sand, soot particles and fibres that can enter through the air intake. In MAN and Mercedes trucks, buses and vans, this filtration stage is essential for the service life of turbochargers, cylinder liners, pistons, piston rings and inlet valves. An air filter element with insufficient filtration, damage or an incorrect fit not only causes increased engine wear, but can also lead to insufficient air supply, loss of power and increased fuel consumption. The correct element must always be identified using the vehicle chassis number. Visual comparison or selection based solely on the model name is never sufficient.

Air filter elements vary considerably depending on the engine family, emission standard, chassis configuration and available installation space. A MAN with a D08, D20, D26 or D38 engine may require a different filter diameter, element height, sealing lip or airflow capacity than a Mercedes with, for example, an OM 904, OM 906, OM 457, OM 471 or OM 473 engine. Variations can also occur within the same engine family due to use in distribution trucks, tractor units, buses or vans.

The most commonly used versions are cylindrical radially sealed air filter elements and panel-type elements. Cylindrical versions generally consist of pleated cellulose filter paper or synthetic fibre media, a metal or plastic inner and outer support, and elastomer seals. The pleat height, effective filter area, pore size of the medium and seal fit together determine the dust holding capacity and airflow resistance. An element with the correct outside diameter but a different seal geometry can allow unfiltered air to pass through at the connection.

When ordering, always check the chassis number, engine code and, where available, the part number. This rules out differences in length, radial seal, end cap design and required air capacity. This is particularly important for high-output turbocharged vehicles, where a filter surface that is too small will more quickly cause excessive intake resistance.

A saturated air filter element usually does not show an immediately visible defect, but causes an increasing pressure drop in the intake airflow. Common symptoms include slow acceleration, reduced power under load, black smoke in older engine generations, increased diesel consumption or fault messages related to air mass, turbo pressure or intake air pressure. In modern Mercedes OM 470, OM 471 and OM 473 engines or MAN D26 and D38 engines, the engine management system may limit the available torque when the measured air mass does not correspond to the requested turbo pressure.

First check the air filter element for crushed pleats, tears in the filter medium, detached end caps, deformed seals and traces of moisture or oil. Oil contamination does not automatically indicate a defective filter element, but it does reduce air permeability and should be considered a replacement criterion. Then inspect the clean-side surface of the element for traces of dust: dust downstream of the filter medium indicates a leak at the seal or a damaged element.

Measure the restriction using a calibrated vacuum gauge or differential pressure gauge on the intake system, at increased engine speed and under load in accordance with the vehicle specification. Compare the measured value with the maximum permissible intake resistance specified by the engine manufacturer. Do not replace the filter element based on appearance alone: a heavily discoloured element may still operate within the pressure-drop limit, while an apparently clean element may already create excessive resistance due to moisture or fine dust loading.

Replace the air filter element preventively in accordance with the maintenance interval, but shorten this interval for construction site traffic, unpaved loading areas, agricultural transport, waste collection or operation in dusty environments. Do not clean paper or synthetic main elements with compressed air: high air velocity can cause microscopic tears and open up the fibre structure, reducing filtration efficiency. Install the new element dry, without grease on the sealing edge, and press it straight and evenly into position to prevent creases or edge leaks.

A correctly selected air filter element limits engine wear and helps prevent unplanned downtime. Based on the chassis number, Braem can assist with the technical identification of suitable air filter elements for MAN and Mercedes vehicles.