FEBI BILSTEIN air filter (40520) maintains peak combustion efficiency by delivering a clean, metered airflow to the intake manifold while blocking dust, pollen, and fine road debris. Filter geometry — Thickness [mm]: 45 mm, Outer Diameter [mm]: 42 mm, External Thread Size: M12 x 1, Rubber — is optimised to maximise surface area within the airbox housing, reducing restriction and extending service intervals without sacrificing filtration efficiency. Cross-references OE filter numbers: 042.429, 1.18365, 1 394 116, 1 411 129 and 6 more. FEBI BILSTEIN air filtration elements are tested to ISO 5011 standards for fractional efficiency, ensuring the engine management system receives clean air data for accurate fuelling across all load points. Air filters should be inspected every 12,000–15,000 miles and replaced when visibly dirty or at least once a year — vehicles driven on dusty or unpaved roads may need more frequent changes. Symptoms of a clogged air filter include reduced acceleration, lower fuel economy, a rough idle, and in extreme cases the engine management light illuminating due to incorrect air-fuel ratios. Replacing an air filter is one of the simplest DIY tasks on any car — usually just unclip the airbox lid, lift out the old element, drop in the new one, and re-seal; no tools required on most vehicles. Choose a filter that matches the OEM filtration efficiency rating (typically 99%+ particle capture) — cheaper filters with lower efficiency let more abrasive particles through to cylinder bores and valve stems. A clean air filter can improve fuel efficiency by up to 10% and helps your engine breathe properly, extending the life of downstream sensors such as the mass airflow meter and oxygen sensors. Every part is dispatched with tracked delivery and a 14-day money-back guarantee with hassle-free returns.

febi bilstein, founded in 1844 in Ennepetal, Germany, is one of the oldest and most comprehensive automotive parts suppliers in the independent aftermarket. febi bilstein offers over 40,000 parts spanning steering, suspension, engine, braking, cooling, and electrical systems. Certified to IATF 16949 and supplying OE-quality components, febi bilstein products undergo rigorous testing to match original equipment performance. With nearly 180 years of German engineering tradition, febi bilstein is the go-to brand for reliable, competitively priced replacement parts.