Filtercase

The air filter housing forms the supporting and sealing part of the air intake system on MAN and Mercedes trucks, buses and vans. This air filter housing positions the air filter element, separates the clean and dirty air sides and directs intake air in a controlled manner to the intake pipe, turbocharger or mass air flow sensor. An intact filter housing is essential: even a small crack, distorted sealing edge or poorly fitting cover can allow unfiltered air to pass through. Abrasive dust particles then cause accelerated wear to compressor wheels, cylinder liners, piston rings and intake valves.

Filter housings vary considerably according to chassis configuration, cab variant, emission standard, available installation space and engine family. For example, air filter housings for MAN D08, D20, D26 and D38 engines have different connection diameters, mounting points and air flow rates than versions for Mercedes OM 906, OM 457, OM 470, OM 471 or OM 473 engines. On buses and vans, the intake position, water separation and resonance damping may also differ from comparable trucks.

An air filter housing generally consists of a lower section, cover, clamps or screw connections, sealing edge, intake connection and an outlet to the clean-air pipe. Depending on the version, dust ejector valves, cyclone pre-separators, restriction indicators and sensor ports may also be fitted. Plastic filter housings are lightweight and corrosion-resistant, but may crack due to age, vibration or incorrect installation. Metal air filter housings are mechanically more robust, but should be checked for corrosion, deformation and damaged weld seams.

The correct air filter housing must always be determined using the vehicle chassis number. Visual comparison or selection based solely on the model name is never sufficient, as similar-looking filter housings may have different connections, filter element lengths, cover latches and mounting brackets.

A damaged air filter housing does not always immediately generate a fault code. In the workshop, the problem often presents itself as increased vacuum in the air intake system, loss of power under load, whistling intake noises, increased fuel consumption or prematurely contaminated air filter elements. Dust traces on the clean side of the filter element are an alarm signal: immediately inspect the complete filter housing, the seal and the connected clean-air pipes towards the turbo.

Start with a visual inspection of the lower section, cover, clamps and all connection sleeves. Check for hairline cracks around mounting lugs and pipe connections, especially on vehicles with high chassis vibrations. Then check that the air filter element sits flush against the sealing edge of the filter housing; a twisted, dented or incorrectly fitted filter element causes bypass leakage. In the event of power complaints, measure the intake restriction using a differential manometer or readable restriction sensor before and after the air filter housing. Compare the measured pressure drop with the vehicle specification at increased engine speed and under load. A low-pressure smoke test helps reveal leaks in the housing, cover seal and outlet intake pipe.

Replace the filter housing when the sealing surfaces are distorted, the clamps provide insufficient clamping force, the plastic wall is cracked or dust has reached the clean side. Do not repair cracks with sealant or adhesive: such repairs are rarely airtight and do not withstand temperature changes, pulsations and vibrations sufficiently. Install a new air filter element in the correct fitting direction, clean the contact surface without abrasive materials and replace damaged seals, clamps and intake sleeves at the same time.

In the event of recurring damage, the mounting bracket should also be checked for metal fatigue, missing rubber mounts and incorrect preload. A correctly identified air filter housing, with technical support for chassis number identification, reduces turbo damage, engine wear and unplanned downtime.