The crankcase ventilation hose routes blow-by gases — combustion gases that leak past the piston rings into the sump area — from the engine block or cam cover back into the inlet manifold or air intake, where they are burnt rather than vented to atmosphere. This closed-loop design has been mandatory on road cars for decades and serves both an emissions function and an engine protection function: without proper scavenging, crankcase pressure builds up and forces oil past seals and gaskets. The hose itself operates in a harsh environment — bathed in oily vapour, subjected to high under-bonnet temperatures, and exposed to vacuum cycling with every change in throttle position. Cracking or perishing of the rubber compound is the most common failure mode, usually first visible as a split near a moulded bend or at one of the clip seats where the hose radius is tightest. A split hose creates an unmetered air leak that the engine management system cannot fully compensate for, resulting in rough idling, hesitation under acceleration, and an illuminated engine warning light. GATES and VAICO both produce ventilation hoses to OE dimensions, with reinforced wall sections at the points most prone to fatigue. Precise OE matching matters because hose routing, connector fittings, and length vary sharply between engine families even within the same vehicle range.
Crankcase ventilation hose configurations differ significantly between engine variants — a 2.0-litre petrol and a 2.0-litre diesel in the same car body often use completely different hose routings and connector types. The OE number linked to your specific engine code is the most precise identifier. Engine codes are stamped on the block and listed on the V5C log book in some markets; alternatively, the make-model-engine selector on this page will filter results to your exact fitment. Hose length and the position of any T-pieces or oil separator connections must all match.
OEM hoses are moulded from an oil-resistant rubber or silicone compound specified for the operating temperature range of that engine. Quality aftermarket hoses from suppliers like GATES use the same material grades and replicate all moulded bends, T-junctions, and connector fittings exactly. Generic aftermarket hoses in universal lengths may not route correctly, causing kinks that restrict flow and accelerate cracking. A poorly fitting hose is as problematic as a cracked one — both introduce uncontrolled air into the intake path.
Yes. In the short term, a cracked hose causes an unmetered air leak that upsets the air-fuel mixture, resulting in rough running and potentially fault codes. Over a longer period, elevated crankcase pressure caused by a blocked or collapsed hose forces oil through the rear main seal, rocker cover gasket, and other low-pressure seals. Some BMW and Audi engines are particularly sensitive, where a failed crankcase breather system is directly implicated in accelerated oil consumption and in extreme cases crankshaft seal failure.
Rough idle that worsens when cold, accompanied by a hissing sound from under the bonnet, is a typical early symptom. A persistent engine management warning light with codes pointing to lean mixture or mass airflow sensor faults is another common presentation. Oil seeping from gaskets or seals — particularly the cam cover or sump — indicates elevated crankcase pressure. Physically inspecting the hose for surface cracks, hardened rubber at the bends, or oil weeping from a clip joint will usually identify the fault visually before symptoms become severe.
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